Modified amine-aldehyde resins and uses thereof in separation processes

ABSTRACT

Modified resins are disclosed for removing a wide variety of solids and/or ionic species from the liquids in which they are suspended and/or dissolved. These modified resins are especially useful as froth flotation depressants in the beneficiation of many types of materials (e.g., mineral and metal ores), including the beneficiation of impure coal comprising clay impurities, as well as in the separation of valuable bitumen from solid contaminants such as sand. The modified resins are also useful for treating aqueous liquid suspensions to facilitate the removal of solid particulates, as well as the removal of metallic ions in the purification of water. The modified resins comprise a base resin that is modified with a coupling agent, which is highly selective for binding to solid contaminants and especially siliceous materials such as sand or clay.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/298,948, filed Dec. 12, 2005 now U.S. Pat No. 7,913,852, which claimsthe benefit of priority of U.S. Provisional Patent Application No.60/638,143, filed Dec. 23, 2004, and Ser. No. 60/713,339, filed Sep. 2,2005, each of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to modified resins for use in separationprocesses, and especially the selective separation of solids and/orionic species such as metallic cations from aqueous media. Suchprocesses include froth flotation (e.g., used in ore beneficiation), theseparation of drill cuttings from oil drilling fluids, clay and coalslurry dewatering, sewage purification, pulp and paper mill effluentprocessing, the removal of sand from bitumen, and the purification ofwater to render it potable. The modified resins comprise a base resinthat is the reaction product of a primary or secondary amine and analdehyde (e.g., a urea-formaldehyde resin). The base resin is modifiedwith a coupling agent (e.g., a substituted silane) during or after itspreparation.

BACKGROUND OF THE INVENTION

Froth Flotation

Industrially, processes for the purification of liquid suspensions ordispersions (and especially aqueous suspensions or dispersions) toremove suspended solid particles are quite prevalent. Froth flotation,for example, is a separation process based on differences in thetendency of various materials to associate with rising air bubbles.Additives are often incorporated into the froth flotation liquid (e.g.,aqueous brine) to improve the selectivity of the process. For example,“collectors” can be used to chemically and/or physically absorb ontomineral(s) (e.g., those comprising value metals) to be floated,rendering them more hydrophobic. On the other hand, “depressants,”typically used in conjunction with collectors, render other materials(e.g., gangue minerals) less likely to associate with the air bubbles,and therefore less likely to be carried into the froth concentrate.

In this manner, some materials (e.g., value minerals or metals) will,relative to others (e.g., gangue materials), exhibit preferentialaffinity for air bubbles, causing them to rise to the surface of theaqueous slurry, where they can be collected in a froth concentrate. Adegree of separation is thereby effected. In less common, so-calledreverse froth flotations, it is the gangue that is preferentiallyfloated and concentrated at the surface, with the desired materialsremoved in the bottoms. Gangue materials typically refer to quartz, sandand clay silicates, and calcite, although other minerals (e.g.,fluorite, barite, etc.,) may be included. In some cases, the material tobe purified comprises predominantly such materials, and the smalleramounts of contaminants are preferentially floated. For example, in thebeneficiation of kaolin clay, a material having a number of industriallysignificant applications, iron and titanium oxides can be separated byflotation from the impure, clay-containing ore, leaving a purifiedkaolin clay bottoms product.

The manner in which known collectors and depressants achieve theireffect is not understood with complete certainty, and several theorieshave been proposed to date. Depressants, for example may prevent thegangue minerals from adhering to the value materials to be separated, orthey may even prevent the collector(s) from absorbing onto the gangueminerals. Whatever the mechanism, the ability of a depressant to improvethe selectivity in a froth flotation process can very favorably impactits economics.

Overall, froth flotation is practiced in the beneficiation of a widevariety of value materials (e.g., mineral and metal ores and even highmolecular weight hydrocarbons such as bitumen), in order to separatethem from unwanted contaminants which are unavoidably co-extracted fromnatural deposits. In the case of solid ore beneficiation, the use offroth flotation generally comprises grinding the crude ore intosufficiently small, discrete particles of a value mineral or metal andthen contacting an aqueous “pulp” of this ground ore with rising airbubbles, typically while agitating the pulp. Prior to froth flotation,the crude ore may be subjected to any number of preconditioning steps,including selective crushing, screening, desliming, gravityconcentration, electrical separation, low temperature roasting, andmagnetic differentiation.

Another particular froth flotation process of commercial significanceinvolves the separation of bitumen from sand and/or clay, which areubiquitous in oil sand deposits, such as those found in the vastAthabasca region of Alberta, Canada. Bitumen is recognized as a valuablesource of “semi-solid” petroleum or heavy hydrocarbon-containing crudeoil, which can be upgraded into many valuable end products includingtransportation fuels such as gasoline or even petrochemicals. Alberta'soil sand deposits are estimated to contain 1.7 trillion barrels ofbitumen-containing crude oil, exceeding the reserves in all of SaudiArabia. For this reason, significant effort has been recently expendedin developing economically feasible operations for bitumen recovery,predominantly based on subjecting an aqueous slurry of extracted oilsand to froth flotation. For example, the “Clark Process” involvesrecovering the bitumen in a froth concentrate while depressing the sandand other solid impurities.

Various gangue depressants for improving froth flotation separations areknown in the art and include sodium silicate, starch, tannins, dextrins,lignosulphonic acids, carboxyl methyl cellulose, cyanide salts and manyothers. More recently certain synthetic polymers have been foundadvantageous in particular beneficiation processes involving frothflotation. For example, U.S. Pat. No. Re. 32,875 describes theseparation of gangue from phosphate minerals (e.g., apatite) using as adepressant a phenol-formaldehyde copolymer (e.g., a resol, a novolak) ora modified phenol polymer (e.g., a melamine-modified novolak).

U.S. Pat. No. 3,990,965 describes the separation of iron oxide frombauxite using as a depressant a water soluble prepolymer of low chainlength that adheres selectively to gangue and that can be furtherpolymerized to obtain a cross-linked, insoluble resin.

U.S. Pat. No. 4,078,993 describes the separation of sulfide or oxidizedsulfide ores (e.g., pyrite, pyrrhotite, or sphalerite) from metalmineral ores (e.g., copper, zinc, lead, nickel) using as a depressant asolution or dispersion of a low molecular weight condensation product ofan aldehyde with a compound containing 2-6 amine or amide groups.

U.S. Pat. Nos. 4,128,475 and 4,208,487 describe the separation of ganguematerials from mineral ore using a conventional frothing agent (e.g.,pine oils) combined with a (preferably alkylated) amino-aldehyde resinthat may have free methylol groups.

U.S. Pat. No. 4,139,455 describes the separation of sulfide or oxidizedsulfide ores (e.g., pyrite, pyrrhotite, or sphalerite) from metalmineral ores (e.g., copper, zinc, lead, nickel) using as a depressant anamine compound (e.g., a polyamine) in which at least 20% of the totalnumber of amine groups are tertiary amine groups and in which the numberof quaternary amine groups is from 0 to not more than ⅓ the number oftertiary amine groups.

U.S. Pat. No. 5,047,144 describes the separation of siliceous materials(e.g., feldspar) from minerals (e.g., kaolinite) using as a depressant acation-active condensation product of aminoplast formers withformaldehyde, in combination with cation-active tensides (e.g., organicalkylamines) or anion-active tensides (e.g,. long-chained alkylsulfonates).

Russian Patent Nos. 427,737 and 276,845 describe the depression of clayslime using carboxymethyl cellulose and urea-formaldehyde resins,optionally combined with methacrylic acid-methacrylamide copolymers orstarch ('845 patent).

Russian Patent Nos. 2,169,740; 2,165,798; and 724,203 describe thedepression of clay carbonate slimes from ores in the potassium industry,including sylvinite (KCl—NaCl) ores. The depressant used is aurea/formaldehyde condensation product that is modified bypolyethylenepolyamine. Otherwise, a guanidine-formaldehyde resin isemployed ('203 patent).

Markin, A. D., et. al., describe the use of urea-formaldehyde resins ascarbonate clay depressors in the flotation of potassium ores. Study ofthe Hydrophilizing Action of Urea-Formaldehyde Resins on Carbonate ClayImpurities in Potassium Ores, Inst. Obshch. Neorg.Khim, USSR, VestsiAkademii Navuk BSSR, Seryya Khimichnykh Navuk (1980); Effect ofUrea-Formaldehyde Resins on the Flotation of Potassium Ores,Khimicheskaya Promyshlennost, Moscow, Russian Federation (1980); andAdsorption of Urea-Formaldehyde Resins on Clay Minerals of PotassiumOres, Inst. Obshch Neorg. Khim., Minsk, USSR, Doklady Akademii Nauk BSSR(1974).

As is recognized in the art, a great diversity of materials can besubject to beneficiation/refinement by froth flotation. Likewise, thenature of both the desired and the unwanted components varies greatly.This is due to the differences in chemical composition of thesematerials, as well as in the types of prior chemical treatment andprocessing steps used. Consequently, the number and type of frothflotation depressants is correspondingly wide.

Also, the use of a given depressant in one service (e.g., raw potassiumore beneficiation) is not a predictor of its utility in an applicationinvolving a significantly different feedstock (e.g., bitumen-containingoil sand). This also applies to any expectation regarding the use of adepressant that is effective in froth flotation, in the any of theseparations of solid contaminants from aqueous liquid suspensions,described below (and vice versa). The theoretical mechanisms by whichfroth flotation and aqueous liquid/solid separations occur aresignificantly different, where the former process relies on differencesin hydrophobicity and the latter on several other possibilities (chargedestabilization/neutralization, agglomeration, host-guest theory(including podands), hard-soft acid base theory, dipole-dipoleinteractions, Highest Occupied Molecular Orbital-Lowest unoccupiedMolecular Orbital (HOMO-LUMO) interactions, hydrogen bonding, Gibbs freeenergy of bonding, etc). Traditional depressants in froth flotation forthe benefication of metallic ores, such as guar gum, are not employed asdewatering agents, or even as depressants in froth flotation for bitumenseparation. Moreover, in two of the applications described below (wasteclay and coal dewatering), no agents are currently used to improve thesolid/liquid separation. Overall, despite the large offering offlotation depressants and dewatering agents in the art, an adequatedegree of refinement in many cases remains difficult to achieve, even,in the case of froth flotation, when two or more sequential “rougher”and “cleaner” flotations are employed. There is therefore a need in theart for agents which can be effectively employed in a wide range ofseparation processes, including both froth flotation and the separationof solid contaminants from liquid suspensions.

Other Separations

Other processes, in addition to froth flotation, for the separation ofsolid contaminants from liquid suspensions can involve the use ofadditives that either destabilize these suspensions or otherwise bindthe contaminants into larger agglomerates. Coagulation, for example,refers to the destabilization of suspended solid particles byneutralizing the electric charge that separates them. Flocculationrefers to the bridging or agglomeration of solid particles together intoclumps or flocs, thereby facilitating their separation by settling orflotation, depending on the density of the flocs relative to the liquid.Otherwise, filtration may be employed as a means to separate the largerflocs.

The additives described above, and especially flocculants, are oftenemployed, for example, in the separation of solid particles of rock ordrill cuttings from oil and gas well drilling fluids. These drillingfluids (often referred to as “drilling muds”) are important in thedrilling process for several reasons, including cooling and lubricatingthe drill bit, establishing a fluid counterpressure to preventhigh-pressure oil, gas, and/or water formation fluids from entering thewell prematurely, and hindering the collapse of the uncased wellbore.Drilling muds, whether water- or oil-based, also remove drill cuttingsfrom the drilling area and transport them to the surface. Flocculantssuch as acrylic polymers are commonly used to agglomerate these cuttingsat the surface of the circulating drilling mud, where they can beseparated from the drilling mud.

Other uses for flocculants in solid/liquid separations include theagglomeration of clays which are suspended in the large waste slurryeffluents from phosphate production facilities. Flocculants such asanionic natural or synthetic polymers, which may be combined with afibrous material such as recycled newspaper, are often used for thispurpose. The aqueous clay slurries formed in phosphate purificationplants typically have a flow rate of over 100,000 gallons per minute andgenerally contain less than 5% solids by weight. The dewatering (orsettling) of this waste clay, which allows for recycle of the water,presents one of the most difficult problems associated with reclamation.The settling ponds used for this dewatering normally make up about halfof the mined area, and dewatering time can be on the order of severalmonths to several years.

In the separation of solids from aqueous liquids, other specificapplications of industrial importance include the filtration of coalfrom water-containing slurries (i.e., coal slurry dewatering), theprocessing of sewage to remove contaminants (e.g., sludge) viasedimentation, and the processing of pulp and paper mill effluents toremove suspended cellulosic solids. The dewatering of coal poses asignificant problem industrially, as the BTU value of coal decreaseswith increasing water content. Raw sewage, both industrial andmunicipal, requires enormous processing capacity, as wastes generated bythe U.S. population, for example, are collected into sewer systems andcarried along by approximately 14 billion gallons of water per day.Paper industry effluent streams likewise represent large volumes ofsolid-containing aqueous liquids, as waste water generated from atypical paper plant often exceeds 25 million gallons per day. Theremoval of sand from aqueous bitumen-containing slurries generated inthe extraction and subsequent processing of oil sands, as describedpreviously, poses another commercially significant challenge in thepurification of aqueous liquid suspensions. Also, the removal ofsuspended solid particulates is often an important consideration in thepurification of water, such as in the preparation of drinking (i.e.,potable) water. Synthetic polyacrylamides, as well asnaturally-occurring hydrocolloidal polysaccharides such as alginates(copolymers of D-mannuronic and L-guluronic acids) and guar gum areconventional flocculants in this service.

The above applications therefore provide several specific examplesrelating to the purification of aqueous liquid suspensions to removesolid particulates. However, such separations are common in a vastnumber of other processes in the mineral, chemical, industrial andmunicipal waste; sewage processing; and paper industries, as well as ina wide variety of other water-consuming industries. Thus, there is aneed in the art for additives that can effectively promote selectiveseparation of a wide variety of solid contaminants from liquidsuspensions. Advantageously, such agents should be selective inchemically interacting with the solid contaminants, through coagulation,flocculation, or other mechanisms such that the removal of thesecontaminants is easily effected. Especially desirable are additives thatare also able to complex unwanted ionic species such as metal cations tofacilitate their removal as well.

SUMMARY OF THE INVENTION

All Uses

The present invention is directed to modified resins for removing,generally in a selective fashion, a wide variety of solids and/or ionicspecies from the liquids in which they are suspended and/or dissolved.These modified resins are especially useful as froth flotationdepressants in the beneficiation of many types of materials includingmineral and metal ores, such as in the beneficiation of kaolin clay. Themodified resins are also useful for treating aqueous liquid suspensions(e.g., aqueous suspensions containing sand, clay, coal, and/or othersolids, such as used drill cutting fluids, as well as process andeffluent streams in phosphate and coal production, sewage treatment,paper manufacturing, or bitumen recovery facilities) to facilitate theremoval of solid particulates and also potentially metallic cations(e.g., in the purification of drinking water) using a number of possibleseparation processes. The modified resins comprise a base resin that ismodified with a coupling agent. The coupling agent is highly selectivefor binding to solid contaminants and especially siliceous materialssuch as sand or clay.

Froth Flotation

Without being bound by theory, the coupling agent is highly selective infroth flotation separations for binding to either gangue or desired(e.g., kaolin clay) materials and especially siliceous gangue materialssuch as sand or clay. Also, because the base resin has affinity forwater, the materials which interact and associate with the couplingagent, are effectively sequestered in the aqueous phase in frothflotation processes. Consequently, the gangue materials can beselectively separated from the value materials (e.g., minerals, metals,or bitumen) or clay-containing ore impurities (e.g., iron and titaniumoxides) that are isolated in the froth concentrate.

Accordingly, in one embodiment, the present invention is a method forbeneficiation of an ore. The method comprises treating a slurry of oreparticles with a depressant comprising a modified resin (i.e., amodified amine-aldehyde resin). The modified resin comprises a baseresin that is the reaction product of a primary or a secondary amine andan aldehyde, and the base resin is modified with a coupling agent. Theore slurry treatment may occur before or during froth flotation. Inanother embodiment, when ore slurry treatment occurs before frothflotation, the treating step comprises combining the slurry of the oreand the depressant, followed by froth flotation of the slurry of the oreand depressant. In another embodiment, the treating step furthercomprises, after the combining step and prior to froth flotation,conditioning the slurry. The conditioning step may be carried out in aconditioning vessel for a conditioning time from about 30 seconds toabout 10 minutes, at a conditioning temperature from about 1° C. toabout 95° C., and at a conditioning pH of at least about 2.0. In anotherembodiment, the beneficiation method purifies and recovers, from theore, a value mineral or metal selected from the group consisting ofphosphate, potash, lime, sulfate, gypsum, iron, platinum, gold,palladium, titanium, molybdenum, copper, uranium, chromium, tungsten,manganese, magnesium, lead, zinc, clay, coal, silver, graphite, nickel,bauxite, borax, and borate. In another embodiment, the ore comprises animpurity selected from the group consisting of sand, clay, an ironoxide, a titanium oxide, iron-bearing titania, mica, ilmenite,tourmaline, an aluminum silicate, calcite, dolomite, anhydrite,ferromagnesian, feldspar, calcium magnesium carbonate, igneous rock,soil, and mixtures thereof. Often, the impurities are sand or clayimpurities, as are typically extracted with phosphate or potassium ores.In another embodiment, however, mercury is an impurity of an orecomprising coal or synthetic gypsum, which is treated with the modifiedresin prior to or during a froth flotation step. The coal or syntheticgypsum has an initial amount of total mercury and the beneficiationpurifies and recovers, from the ore, purified coal or purified syntheticgypsum having a final amount of total mercury that is less than theinitial amount of total mercury, wherein the initial and final amountsof total mercury are measured on a volatile free basis. In anotherembodiment, the final amount of total mercury is less than about 10 ppbon a volatile free basis. In another embodiment, the synthetic gypsum isformed during desulfurization of flue gas from a coal-burning powerplant. In another embodiment, the depressant comprises the modifiedresin and a chelating agent. In another embodiment, the ore comprises animpure coal ore, the treating step is prior to or during a frothflotation step, and the beneficiation purifies and recovers, from theimpure coal ore, purified coal having, relative to the impure coal ore,a reduced amount of an impurity selected from the group consisting ofnitrogen, sulfur, silicon, ash, and pyrite, wherein the impurity ismeasured on a volatile free weight basis. In another embodiment, the orecomprises an impure coal ore, the treating step is prior to or during afroth flotation step, and the beneficiation purifies and recovers, fromthe impure coal ore, purified coal having, relative to the impure coalore, a reduced amount of moisture and/or an increased BTU value per unitweight.

In another embodiment, the base resin is a urea-formaldehyde resin. Inanother embodiment, the coupling agent is selected from the groupconsisting of a substituted silane, a silicate, silica, a polysiloxane,and mixtures thereof.

In another embodiment, the present invention is a froth flotationdepressant for beneficiation of value materials, including minerals orvalue metal ores. The depressant comprises a modified resin in asolution or dispersion having a resin solids content from about 0.1% toabout 90% by weight, often from about 30% to about 90% by weight. Inanother embodiment, the resin solids content may be greater than about90% by weight, and the modified resin may be employed in forms such as asolid powder, prill, lump, flake, or a melt. The modified resincomprises a base resin that is the reaction product of a primary orsecondary amine and an aldehyde. The base resin is modified with acoupling agent. The coupling agent is present in an amount representingfrom about 0.1% to about 2.5% of the weight of the solution ordispersion, having a resin solids content from about 30% to about 90% byweight. In another embodiment, the base resin is a urea-formaldehyderesin that is the reaction product of urea and formaldehyde at aformaldehyde : urea (F:U) molar ratio from about 1.75:1 to about 3:1. Inanother embodiment, the base resin comprises a urea-formaldehyde resinhaving a number average molecular weight (M_(n)) of greater than about100 grams/mole, and often from about 400 to about 4000 grams/mole. Inanother embodiment, the coupling agent is a substituted silane selectedfrom the group consisting of a ureido substituted silane, an aminosubstituted silane, a sulfur substituted silane, an epoxy substitutedsilane, a methacryl substituted silane, a vinyl substituted silane, analkyl substituted silane, and a haloalkyl substituted silane.

In another embodiment, the present invention is a method for purifyingclay from a clay-containing ore comprising an impurity selected from ametal, a metal oxide, a mineral, and mixtures thereof. The methodcomprises treating a slurry of the clay-containing ore with a depressantcomprising a modified resin and recovering, by froth flotation of theimpurity either after or during the treating step, a purified clayhaving a reduced amount at least one of the impurities. The modifiedresin comprises a base resin that is the reaction product of a primaryor a secondary amine and an aldehyde. The base resin is modified with acoupling agent. In another embodiment, the clay-containing ore compriseskaolin clay. In another embodiment, the impurity comprises a mixture ofiron oxide and titanium dioxide. In another embodiment, the impuritycomprises coal.

In another embodiment, the present invention is a method for purifyingbitumen from a bitumen-containing slurry comprising sand or clay. Themethod comprises treating the slurry with a depressant comprising themodified resin described above and recovering, by froth flotation eitherafter or during the treating step, purified bitumen having a reducedamount of sand or clay.

Other Separadons

In another embodiment, the present invention is a method for purifyingan aqueous liquid suspension comprising a solid contaminant. The methodcomprises treating the liquid suspension with a modified resin asdescribed above and removing, either after or during the treating step,(1) at least a portion of the solid contaminant in a contaminant-richfraction and/or (2) a purified liquid. In another embodiment, thetreating step comprises flocculating the solid contaminant (e.g., sandor clay). In another embodiment, the removing step is carried out bysedimentation, flotation, or filtration. In another embodiment, theliquid suspension is an oil well drilling fluid and the method comprisesremoving a purified drilling fluid for reuse in oil well drilling. Inanother embodiment, the aqueous liquid suspension is a clay-containingeffluent slurry from a phosphate production facility and the methodcomprises removing purified water for reuse in phosphate production. Inanother embodiment, the aqueous liquid suspension is an aqueouscoal-containing suspension and the method comprises removing a coal-richfraction by filtration. In another embodiment, the aqueous liquidsuspension comprises sewage and the method comprises removing purifiedwater by sedimentation. In another embodiment, the aqueous liquidsuspension comprises a pulp or paper mill effluent, the solidcontaminant comprises a cellulosic material, and the method comprisesremoving purified water. In another embodiment, the aqueous liquidsuspension is a bitumen production process intermediate or effluentslurry comprising sand or clay. In still another embodiment, thepurified liquid is potable water.

In another embodiment, the present invention is a method for purifyingcoal ore. The method comprises treating an aqueous slurry of the coalore with a depressant prior to or during a size or densityclassification operation which recovers purified coal having, relativeto the coal ore, a reduced amount of an impurity selected from the groupconsisting of mercury, nitrogen, sulfur, silicon, ash, and pyrite,wherein the impurity is measured on a volatile free basis. Thedepressant comprises a modified resin as described herein. In anotherembodiment, the purified coal has, relative to the coal ore, a reducedamount of moisture and/or an increased BTU value per unit weight. Inanother embodiment, the purified coal has, relative to the coal ore, areduced amount of all impurities selected from the group consisting ofmercury, nitrogen, sulfur, silicon, ash, and pyrite. In anotherembodiment, the reduced amount is less than an amount in a purifiedreference coal recovered in the size classification operation, butwithout treating the aqueous slurry with the depressant. In anotherembodiment, the size or density classification operation is selectedfrom the group consisting of a cyclone separation, a heavy mediumseparation, filtration, screening, and combinations thereof.

In another embodiment, the present invention is a method for purifyingwater comprising a metallic cation. The method comprises treating thewater with the modified resin described above and removing at least aportion of the metallic cation by filtration to yield purified water(e.g., potable water). In another embodiment, the removing stepcomprises membrane filtration. In another embodiment, the metalliccation is selected from the group consisting of As⁺⁵, Pb⁺², Cd⁺², Cu⁺²,Mn⁺², Hg⁺², Zn⁺², Fe⁺², and mixtures thereof. In yet another embodiment,the base resin is further modified with an anionic functional group.

These and other embodiments are apparent from the following DetailedDescription.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates the performance, in the flotation of a sample ofground potassium ore, of silane coupling agent-modifiedurea-formaldehyde resins having a molecular weight within the range of400-1200 grams/mole. The performance is shown relative to unmodifiedresins (i.e., without an added silane coupling agent) and also relativeto a guar gum control sample.

DETAILED DESCRIPTION OF THE INVENTION

All Uses

The modified resin that is used in separation processes of the presentinvention comprises a base resin that is the reaction product of aprimary or secondary amine and an aldehyde. The primary or secondaryamine, by virtue of having a nitrogen atom that is not completelysubstituted (i.e., that is not part of a tertiary or quaternary amine)is capable of reacting with an aldehyde, to form an adduct. Ifformaldehyde is used as the aldehyde, for example, the adduct is amethylolated adduct having reactive methylol functionalities. Forpurposes of the present invention, representative primary and secondaryamines used to form the base resin include compounds having at least twofunctional amine or amide groups, or amidine compounds having at leastone of each of these groups. Such compounds include ureas, guanidines,and melamines, which may be substituted at their respective aminenitrogen atoms with aliphatic or aromatic radicals, wherein at least twonitrogen atoms are not completely substituted. Primary amines are oftenused. Representative of these is urea, which has a low cost and isextensively available commercially. In the case of urea, if desired, atleast a portion thereof can be replaced with ammonia, primaryalkylamines, alkanolamines, polyamines (e.g., alkyl primary diaminessuch as ethylene diamine and alkyl primary triamines such as diethylenetriamine), polyalkanolamines, melamine or other amine-substitutedtriazines, dicyandiamide, substituted or cyclic ureas (e.g., ethyleneurea), primary amines, secondary amines and alkylamines, tertiary aminesand alkylamines, guanidine, and guanidine derivatives (e.g.,cyanoguanidine and acetoguanidine). Aluminum sulfate, cyclic phosphatesand cyclic phosphate esters, formic acid or other organic acids may alsobe used in conjunction with urea. The amount of any one of thesecomponents (or if used in combination then their combined amount), ifincorporated into the resin to replace part of the urea, typically willvary from about 0.05 to about 20% by weight of the resin solids. Thesetypes of agents promote hydrolysis resistance, flexibility, reducedaldehyde emissions and other characteristics, as is appreciated by thosehaving skill in the art.

The aldehyde used to react with the primary or secondary amine asdescribed above, to form the base resin, may be formaldehyde, or otheraliphatic aldehydes such as acetaldehyde and propionaldehyde. Aldehydesalso include aromatic aldehydes (e.g., benzylaldehyde and furfural), andother aldehydes such as aldol, glyoxal, and crotonaldehyde. Mixtures ofaldehydes may also be used. Generally, due to its commercialavailability and relatively low cost, formaldehyde is used.

In forming the base resin, the initial formation of an adduct betweenthe amine and the aldehyde is well known in the art. The rate of thealdehyde addition reaction is generally highly dependent on pH and thedegree of substitution achieved. For example, the rate of addition offormaldehyde to urea to form successively one, two, and three methylolgroups has been estimated to be in the ratio of 9:3:1, whiletetramethylolurea is normally not produced in a significant quantity.The adduct formation reaction typically proceeds at a favorable rateunder alkaline conditions and thus in the presence of a suitablealkaline catalyst (e.g., ammonia, alkali metal hydroxides, or alkalineearth metal hydroxides). Sodium hydroxide is most widely used.

At sufficiently high pH values, it is possible for the adduct formationreaction to proceed essentially in the absence of condensation reactionsthat increase the resin molecular weight by polymerization (i.e., thatadvance the resin). However, for the formation of low molecular weightcondensate resins from the further reaction of the amine-aldehydeadduct, the reaction mixture is generally maintained at a pH of greaterthan about 5 and typically from about 5 to about 9. If desired, an acidsuch as acetic acid can be added to help control the pH and thereforethe rate of condensation and ultimately the molecular weight of thecondensed resin. The reaction temperature is normally in the range fromabout 30° C. to about 120° C., typically less than about 85° C., andoften the reflux temperature is used. A reaction time from about fromabout 15 minutes to about 3 hours, and typically from about 30 minutesto about 2 hours, is used in preparing the low molecular weightamine-aldehyde condensate resin from the primary or secondary amine andaldehyde starting materials.

Various additives may be incorporated, prior to or during thecondensation reaction, in order to impart desired properties into thefinal modified amine-aldehyde resin. For example, guar gum;carboxymethylcellulose or other polysaccharides such as alginates; orpolyols such as polyvinyl alcohols, pentaerythitol, or Jeffol™ polyols(Hunstman Corporation, Salt Lake City, Utah, USA) may be used to alterthe viscosity and consistency of the amine-aldehyde resin condensate,which when used to prepare the modified amine-aldehyde resin, canimprove its performance in froth flotation and other applications.Otherwise, quaternary ammonium salts including diallyl dimethyl ammoniumchloride (or analogs such as diallyl diethyl ammonium chloride) oralkylating agents including epichlorohydrin (or analogs such asepibromohydrin) may be used to increase the cationic charge of theamine-aldehyde resin condensate, which when used to prepare the modifiedamine-aldehyde resin, can improve its performance in certainsolid/liquid separations (e.g., clay dewatering) discussed below. Inthis manner, such additives may be more effectively reacted into themodified amine-aldehyde resin than merely blended with the resin afterits preparation.

Condensation reaction products of the amine-aldehyde, amide-aldehyde,and/or amidine-aldehyde adducts described above include, for examplethose products resulting from the formation of (i) methylene bridgesbetween amido nitrogens by the reaction of alkylol and amino groups,(ii) methylene ether linkages by the reaction of two alkylol groups,(iii) methylene linkages from methylene ether linkages with thesubsequent removal of formaldehyde, and (iv) methylene linkages fromalkylol groups with the subsequent removal of water and formaldehyde.

Generally, in preparing the base resin, the molar ratio ofaldehyde:primary or secondary amine is from about 1.5:1 to about 4:1,which refers to the ratio of moles of all aldehydes to moles of allamines, amides, and amidines reacted to prepare the base resin duringthe course of the adduct formation and condensation reactions describedabove, whether performed separately or simultaneously. The resin isnormally prepared under ambient pressure. The viscosity of the reactionmixture is often used as a convenient proxy for the resin molecularweight. Therefore the condensation reaction can be stopped when adesired viscosity is achieved after a sufficiently long time and at asufficiently high temperature. At this point, the reaction mixture canbe cooled and neutralized. Water may be removed by vacuum distillationto give a resin with a desired solids content. Any of a wide variety ofconventional procedures used for reacting primary and secondary amineand aldehyde components can be used, such as staged monomer addition,staged catalyst addition, pH control, amine modification, etc., and thepresent invention is not limited to any particular procedure.

A representative base resin for use in separation processes of thepresent invention is a urea-formaldehdye resin. As described above, aportion of the urea may be replaced by other reactive amine and/oramides and a portion of the formaldehyde may be replaced by otheraldehydes, to provide various desirable properties, without departingfrom the characterization of the base resin as a urea-formaldehyderesin. Urea-formaldehyde resins, when used as the base resin, can beprepared from urea and formaldehyde monomers or from precondensates inmanners well known to those skilled in the art. Generally, the urea andformaldehyde are reacted at a molar ratio of formaldehyde to urea (F:U)in the range from about 1.75:1 to about 3:1, and typically at aformaldehyde:urea (F:U) mole ratio from about 2:1 to about 3:1, in orderto provide sufficient methylolated species for resin cross-linking(e.g., di- and tri-methylolated ureas). Generally, the urea-formaldehyderesin is a highly water dilutable dispersion, if not an aqueoussolution.

In various embodiments, the condensation is allowed to proceed to anextent such that the urea-formaldehyde base resin has a number averagemolecular weight (M_(n)), of greater than about 100 grams/mole, andoften greater than about 300 grams/mole. Good results in separationprocesses have been achieved with urea-formaldehyde base resin molecularweights in the range from about 400 to about 4000 grams/mole and also inthe range from about 400 to about 1200 grams/mole. As is known in theart, the value of M_(n) of a polymer sample having a distribution ofmolecular weights is defined as

${M_{n} = \frac{\sum\limits_{i}{N_{i}M_{i}}}{\sum\limits_{i}N_{i}}},$

where N_(i) is the number of polymer species having i repeat units andM_(i) is the molecular weight of the polymer species having i repeatunits. The number average molecular weight is typically determined usinggel permeation chromatography (GPC), using solvent, standards, andprocedures well known to those skilled in the art.

A cyclic urea-formaldehyde resin may also be employed and prepared, forexample, according to procedures described in U.S. Pat. No. 6,114,491.Urea, formaldehyde, and ammonia reactants are used in a mole ratio ofurea:formaldehyde:ammonia that may be about 0.1 to 1.0:about 0.1 to3.0:about 0.1 to 1.0. These reactants are charged to a reaction vesselwhile maintaining the temperature below about 70° C. (160° F.), oftenabout 60° C. (140° F.). The order of addition is not critical, but it isimportant to take care during the addition of ammonia to formaldehyde(or formaldehyde to ammonia), due to the exothermic reaction. In fact,due to the strong exotherm, it may be preferred to charge theformaldehyde and the urea first, followed by the ammonia. This sequenceof addition allows one to take advantage of the endotherm caused by theaddition of urea to water to increase the rate of ammonia addition. Abase may be required to maintain an alkaline condition throughout thecook.

Once all the reactants are in the reaction vessel, the resultingsolution is heated at an alkaline pH to between about 60 and 105° C.(about 140 to about 220° F.), often about 85 to 95° C. (about 185 to205° F.), for 30 minutes to 3 hours, depending on mole ratio andtemperature, or until the reaction is complete. Once the reaction iscomplete, the solution is cooled to room temperature for storage. Theresulting solution is storage stable for several months at ambientconditions. The pH is between 5 and 11.

The yield is usually about 100%. The cyclic urea resins often contain atleast 20% triazone and substituted triazone compounds. The ratio ofcyclic ureas to di- and tri- substituted ureas and mono-substitutedureas varies with the mole ratio of the reactants. For example, a cyclicurea resin having the mole ratio of 1.0:2.0:0.5 U:F:A resulted in asolution characterized by C¹³-NMR and containing approximately 42.1%cyclic ureas, 28.5% di/tri-substituted ureas, 24.5% mono-substitutedureas, and 4.9% free urea. A cyclic urea resin having the mole ratio of1.0:1.2:0.5 U:F:A resulted in a solution characterized by C¹³-NMR andcontaining approximately 25.7% cyclic ureas, 7.2% di/tri-substitutedureas, 31.9% mono-substituted ureas, and 35.2 free urea.

In addition, the cyclic urea-formaldehyde resin may be prepared by amethod such as described in U.S. Pat. No. 5,674,971. The cyclic urearesin is prepared by reacting urea and formaldehyde in at least a twostep and optionally a three-step process. In the first step, conductedunder alkaline reaction conditions, urea and formaldehyde are reacted inthe presence of ammonia, at an F/U mole ratio of between about 1.2:1 and1.8:1. The ammonia is supplied in an amount sufficient to yield anammonia/urea mole ratio of between about 0.05:1 and 1.2:1. The mixtureis reacted to form a cyclic triazone/triazine or cyclic urea resin.

Water soluble triazone compounds may also be prepared by reacting urea,formaldehyde and a primary amine as described in U.S. Pat. Nos.2,641,584 and 4,778,510. These patents also describe suitable primaryamines such as, but are not limited to, alkyl amines such as methylamine, ethyl amine, and propyl amine, lower hydroxyamines such asethanolamine cycloalkylmonoamines such as cyclopentylamine,ethylenediamine, hexamethylenediamine, and linear polyamines. Theprimary amine may be substituted or unsubstituted.

In the case of a cyclic urea-formaldehyde or a urea-formaldehyde resin,skilled practitioners recognize that the urea and formaldehyde reactantsare commercially available in many forms. Any form which is sufficientlyreactive and which does not introduce extraneous moieties deleterious tothe desired reactions and reaction products can be used in thepreparation of urea-formaldehyde resins useful in the invention. Forexample, commonly used forms of formaldehyde include paraform (solid,polymerized formaldehyde) and formalin solutions (aqueous solutions offormaldehyde, sometimes with methanol, in 37 percent, 44 percent, or 50percent formaldehyde concentrations). Formaldehyde also is available asa gas. Any of these forms is suitable for use in preparing aurea-formaldehyde base resin. Typically, formalin solutions are used asthe formaldehyde source. To prepare the base resin of the presentinvention, formaldehyde may be substituted in whole or in part with anyof the aldehydes described above (e.g., glyoxal).

Similarly, urea is commonly available in a variety of forms. Solid urea,such as prill, and urea solutions, typically aqueous solutions, arecommercially available. Any form of urea is suitable for use in thepractice of the invention. For example, many commercially preparedurea-formaldehyde solutions may be used, including combinedurea-formaldehyde products such as Urea-Formaldehyde Concentrate (e.g.,UFC 85) as disclosed in U.S. Pat. Nos. 5,362,842 and 5,389,716.

Also, urea-formaldehyde resins such as the types sold by Georgia PacificResins, Inc., Borden Chemical Co., and Neste Resins Corporation may beused. These resins are prepared as either low molecular weightcondensates or as adducts which, as described above, contain reactivemethylol groups that can undergo condensation to form resin polymers,typically within the number average molecular weight ranges describedpreviously. The resins will generally contain small amounts of unreacted(i.e., free) urea and formaldehyde, as well as cyclic ureas,mono-methylolated urea, and di- and tri-methylolated ureas. The relativequantities of these species can vary, depending on the preparationconditions (e.g., the molar formaldehyde:urea ratio used). The balanceof these resins is generally water, ammonia, and formaldehyde. Variousadditives known in the art, including stabilizers, cure promoters,fillers, extenders, etc., may also be added to the base resin.

Modified resins of the present invention are prepared by modifying thebase resin, as described above, with a coupling agent that is highlyselective for binding with unwanted solid materials (e.g., sand or clay)and/or ionic species such as metallic cations to be separated in theseparation/purification processes of the present invention. Withoutbeing bound by theory, the coupling agent is believed to improve theability of the base resin, which, in one embodiment, is generallycationic (i.e., carries more overall positive than negative charge) toattract most clay surfaces, which are generally anionic (i.e., carrymore overall negative than positive charge). These differences inelectronic characteristics between the base resin and clay can result inmutual attraction at multiple sites and even the potential sharing ofelectrons to form covalent bonds. The positive-negative chargeinteractions which cause clay particles to become attracted to the baseresin is potentially explained by several theories, such as host-guesttheory (including podands), hard-soft acid base theory, dipole-dipoleinteractions, and Highest Occupied Molecular Orbital-Lowest unoccupiedMolecular Orbital (HOMO-LUMO) interactions, hydrogen bonding, Gibbs freeenergy of bonding, etc.

The coupling agent may be added before, during, or after theadduct-forming reaction, as described above, between the primary orsecondary amine and the aldehyde. For example, the coupling agent may beadded after an amine-aldehyde adduct is formed under alkalineconditions, but prior to reducing the pH of the adduct (e.g., byaddition of an acid) to effect condensation reactions. Normally, thecoupling agent is covalently bonded to the base resin by reactionbetween a base resin-reactive functional group of the coupling agent anda moiety of the base resin.

The coupling agent may also be added after the condensation reactionsthat yield a low molecular weight polymer. For example, the couplingagent may be added after increasing the pH of the condensate (e.g., byaddition of a base) to halt condensation reactions. Advantageously, ithas been found that the base resin may be sufficiently modified byintroducing the coupling agent to the resin condensate at an alkaline pH(i.e., above pH 7), without appreciably advancing the resin molecularweight. Typically, the resin condensate is in the form of an aqueoussolution or dispersion of the resin. When substituted silanes are usedas coupling agents, they can effectively modify the base resin underalkaline conditions and at either ambient or elevated temperatures. Anytemperature associated with adduct formation or condensate formationduring the preparation of the base resin, as described above, issuitable for incorporation of the coupling agent to modify the baseresin. Thus, the coupling agent may be added to the amine-aldehydemixture, adduct, or condensate at a temperature ranging from ambient toabout 100° C. Generally, an elevated temperature from about 35° C. toabout 45° C. is used to achieve a desirable rate of reaction, forexample, between the base resin-reactive group of the substituted silaneand the base resin itself. As with the resin condensation reactionsdescribed previously, the extent of this reaction may be monitored bythe increase in the viscosity of the resin solution or dispersion overtime.

Alternatively, in some cases a silane coupling agent may be added to theliquid that is to be purified (e.g., the froth flotation slurry) andthat contains the base resin, in order to modify the base resin in situ.

Representative coupling agents that can modify the base resin of thepresent invention and that also have the desired binding selectivity oraffinity for impurities such as sand, clay, and/or ionic species includesubstituted silanes, which posses both a base resin-reactive group(e.g., an organofunctional group) and a second group (e.g., atrimethoxysilane group) that is capable of adhering to, or interactingwith, unwanted impurities (especially siliceous materials). Withoutbeing bound by theory, the second group may effect the agglomeration ofthese impurities into larger particles or flocs (i.e., by flocculation),upon treatment with the modified resin. This facilitates their removal.In the case of ore froth flotation separations, this second group of thecoupling agent promotes the sequestering of either gangue impurities ordesired materials (e.g., kaolin clay) in the aqueous phase, in which thebase resin is soluble or for which the base resin has a high affinity.This improves the separation of value materials from the aqueous phaseby flotation with a gas such as air.

Representative base resin-reactive groups of the silane coupling agentsinclude, but are not limited to, ureido-containing moieties (e.g.,ureidoalkyl groups), amino-containing moieties (e.g., aminoalkylgroups), sulfur-containing moieties (e.g., mercaptoalkyl groups),epoxy-containing moieties (e.g., glycidoxyalkyl groups),methacryl-containing moieties (e.g., methacryloxyalkyl groups),vinyl-containing moieties (e.g., vinylbenzylamino groups),alkyl-containing moieties (e.g., methyl groups), or haloalkyl-containingmoieties (e.g., chloroalkyl groups). Representative substituted silanecoupling agents of the present invention therefore include ureidosubstituted silanes, amino substituted silanes, sulfur substitutedsilanes, epoxy substituted silanes, methacryl substituted silanes, vinylsubstituted silanes, alkyl substituted silanes, and haloalkylsubstituted silanes.

It is also possible for the silane coupling agent to be substituted withmore than one base-resin reactive group. For example, the tetravalentsilicon atom of the silane coupling agent may be independentlysubstituted with two or three of the base-resin reactive groupsdescribed above. As an alternative to, or in addition to, substitutionwith multiple base-resin reactive groups, the silane coupling agent mayalso have multiple silane functionalities, to improve the strength orcapacity of the coupling agent in bonding with either gangue impuritiessuch as sand or desired materials such as kaolin clay. The degree ofsilylation of the silane coupling agent can be increased, for example,by incorporating additional silane groups into coupling agent or bycross-linking the coupling agent with additional silane-containingmoieties. The use of multiple silane functionalities may even result ina different orientation between the coupling agent and clay surface(e.g., affinity between the clay surface and multiple silane groups atthe “side” of the coupling agent, versus affinity between a singlesilane group at the “head” of the coupling agent).

The silane coupling agents also comprise a second group, as describedabove, which includes the silane portion of the molecule, that istypically substituted with one or more groups selected from alkoxy(e.g., trimethoxy), acyloxy (e.g., acetoxy), alkoxyalkoxy (e.g.,methoxyethoxy), aryloxy (e.g., phenoxy), aroyloxy (e.g., benzoyloxy),heteroaryloxy (e.g., furfuroxy), haloaryloxy (e.g., chlorophenoxy),heterocycloalkyloxy (e.g., tetrahydrofirfuroxy), and the like.Representative silane coupling agents, having both base resin-reactivegroups and second groups (e.g., gangue-reactive groups) as describedabove, for use in modifying the base resin, therefore includeureidopropyltrimethoxysilane, ureidopropyltriethoxysilane,aminopropyltrimethoxysilane, aminopropyltriethoxysilane,aminopropylmethyldiethoxysilane, aminopropylmethyldimethoxysilane,aminoethylaminopropyltrimethoxysilane,aminoethylaminopropyltriethoxysilane,aminoethylaminopropylmethyldimethoxysilane,diethylenetriaminopropyltrimethoxysilane,diethylenetriaminopropyltriethoxysilane,diethylenetriaminopropylmethyldimethoxysilane,diethylenetriaminopropylmethyldiethoxysilane,cyclohexylaminopropyltrimethoxysilane,hexanediaminomethyltriethoxysilane, anilinomethyltrimethoxysilane,anilinomethyltriethoxysilane, diethylaminomethyltriethoxysilane,(diethylaminomethyl)methyldiethoxysilane,methylaminopropyltrimethoxysilane,bis(triethoxysilylpropyl)tetrasulfide,bis(triethoxysilylpropyl)disulfide, mercaptopropyltrimethoxysilane,mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane,3-thiocyanatopropyltriethoxysilane, isocyanatopropyl triethylsilane,glycidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane,glycidoxypropylmethyldiethoxysilane,glycidoxypropylmethyldimethoxysilane,methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane,methacryloxypropylmethyldimethoxysilane, chloropropyltrimethoxysilane,chloropropyltriethoxysilane, chloromethyltriethoxysilane,chloromethyltrimethoxysilane, dichloromethyltriethoxysilane,vinyltrimethoxysilane, vinyltriethoxysilane,vinyltris(2-methoxyethoxy)silane, vinyltriacetoxysilane,alkylmethyltrimethoxysilane, vinylbenzylaminotrimethoxysilane,(3,4-epoxycyclohexyl)ethyltrimethoxysilane, aminopropyltriphenoxysilane,aminopropyltribenzoyloxysilane, aminopropyltrifurfuroxysilane,aminopropyltri(o-chlorophenoxy)silane,aminopropyltri(p-chlorophenoxy)silane,aminopropyltri(tetrahydrofurfuroxy)silane, ureidosilane,mercaptoethyltriethoxysilane, and vinyltrichlorosilane,methacryloxypropyltri(2-methoxyethoxy)silane.

Other representative silane coupling agents include oligomericaminoalkylsilanes having, as a base resin-reactive group, two or morerepeating aminoalkyl or alkylamino groups bonded in succession. Anexample of an oligomeric aminoalkylsilane is the solution Silane A1106,available under the trade name Silquest (GE Silicones-OSi Specialties,Wilton, Conn., USA), which is believed to have the general formula(NH₂CH₂CH₂CH₂SiO_(1.5))_(n), wherein n is from 1 to about 3. Modifiedaminosilanes such as a triaminosilane solution (e.g., Silane A1128,available under the same trade name and from the same supplier) may alsobe employed.

Other representative silane coupling agents are the ureido substitutedand amino substituted silanes as described above. Specific examples ofthese are ureidopropyltrimethoxysilane, ureidopropyltriethoxysilane,aminopropyltrimethoxysilane, and aminopropyltriethoxysilane.

Polysiloxanes and polysiloxane derivatives may also be used as couplingagents, as described above, to enhance the performance of the modifiedbase resin in solid/liquid separations. Polysiloxane derivatives includethose polyorganosiloxanes obtained from the blending of organic resinswith polysiloxane resins to incorporate various functionalities therein,including urethane, acrylate, epoxy, vinyl, and alkyl functionalities.

Silica and/or silicates may be used in conjunction (e.g., added as ablending component) with the modified resin of the present invention topotentially improve its affinity for either gangue impurities or desiredmaterials (e.g., kaolin clay), especially siliceous materials includingsand and clay. Other agents that may be used to improve the performanceof modified resins in the separation processes of the present inventioninclude polysaccharides, polyvinyl alcohol, polyacrylamide, as well asknown flocculants (e.g., alginates). These agents can likewise be usedwith modified urea-formaldehyde resins wherein, as described above, atleast a portion of the urea is replaced with ammonia or an amine asdescribed above (e.g., primary alkylamines, alkanolamines, polyamines,etc.). Otherwise, such agents can also be used with the modified resins,which are further modified with anionic functional groups (e.g.,sulfonate) or stabilized by reaction with an alcohol (e.g., methanol),as described below.

Silica in the form of an aqueous silica sol, for example, is availablefrom Akzo Nobel under the Registered Trademark “Bindzil” or from DuPontunder the Registered Trademark “Ludox”. Other grades of sol areavailable having various particle sizes of colloidal silica andcontaining various stabilizers. The sol can be stabilized by alkali, forexample sodium, potassium, or lithium hydroxide or quaternary ammoniumhydroxide, or by a water-soluble organic amine such as alkanolamine.

Silicates, such as alkali and alkaline earth metal silicates (e.g.,lithium silicate, sodium-lithium silicate, potassium silicate, magnesiumsilicate, and calcium silicate), as well as ammonium silicate or aquaternary ammonium silicate, may also be used in the preparation of amodified resin. Additionally, stabilized colloidal silica-silicateblends or mixtures, as described in U.S. Pat. No. 4,902,442, areapplicable.

In the separation processes of the present invention, particularly goodperformance has been found when preparing the modified resin using anamount of coupling agent representing from about 0.01% to about 5% ofthe weight of a solution or dispersion of the base resin, having asolids content from about 30% to about 90%, typically from about 45% toabout 70%. In general, lower amounts of coupling agent addition do notachieve appreciable modification of the base resin, while higher amountsdo not improve performance enough to justify the cost of the addedcoupling agent. When a mixture of coupling agents is used, the totalweight of the mixture is normally within this range. An especiallydesired amount of added coupling agent is from about 0.1% to about 2.5%of the weight of a base resin solution or dispersion having a solidscontent within the range given above.

Alternatively, regardless of the solids content of the base resinsolution or dispersion, the coupling agent is generally employed in anamount from about 0.01% to about 17%, and typically from about 0.1% toabout 8.3%, of the weight of the base resin solids. These representativeranges of added coupling agent, based on the weight of the base resinitself, apply not only to resin solutions or dispersions, but also to“neat” forms of the modified base resin having little or no addedsolvent or dispersing agent (e.g., water). These ranges also generallyapply when the basis is the combined weight of amine and aldehyde, asdescribed previously, that is reacted to form the base resin. Generally,at least about 90% by weight, and typically at least about 95% byweight, of these amine and aldehyde components are reacted, in order toreduce the amounts of free, unreacted amine and aldehyde components,thereby more efficiently utilizing them in the production of the baseresin polymer, and minimizing any deleterious effects (e.g.,vaporization into the environment) associated with these components intheir free form. As described previously, the modified resin may also beprepared by adding the coupling agent to the reaction mixture of amineand aldehyde used to form the base resin. The optimal amount of couplingagent is dependent on a number of factors, including the base resinsolids content, the type of base resin and the particular couplingagent, the purity of the raw ore slurry to be beneficiated or liquidsuspension to be purified, etc.

Modified amine-aldehyde resins for use in separation processes of thepresent invention may be employed in the form of a solution ordispersion having a resin solids content generally ranging from about0.1% to about 90% by weight. Typical modified amine-aldehyde resinscontain from about 40% to about 100% resin solids or non-volatiles, andoften from about 55% to about 75% non-volatiles. Such resins may,however, be diluted to a lower solids content (e.g., below about 30% byweight), for example, using a brine solution together with a thickenersuch as poly(acrylic acid) for storage. The non-volatiles content ismeasured by the weight loss upon heating a small (e.g., 1-5 gram),sample of the composition at about 105° C. for about 3 hours. When anessentially “neat” form of the modified resin, having few or no volatilecomponents, is employed, the pure resin may be added to the frothflotation slurry or liquid dispersion to be purified, such that anaqueous resin solution or dispersion is formed in situ. Neat forms ofthe modified amine-aldehyde resins may be obtained from solutions ordispersions of these resins using conventional drying techniques, forexample spray drying. In some cases, a resin solids content of greaterthan about 90% by weight may be used. Forms of the modifiedamine-aldehyde resin at such high solids levels include viscous liquids,gels, melts, or solid forms including prill, lump, flake, or powderssuch as spray dried materials.

Aqueous solutions or dispersions of the modified resins of the presentinvention will generally be a clear liquid or a liquid having a white oryellow appearance. They will typically have a Brookfield viscosity fromabout 75 to about 500 cps and a pH from about 6.5 to about 9.5. The freeformaldehyde content and free urea content of urea-formaldehyde resinsolutions typically are each below 5%, and usually are each below 3%,and often are each below 1%. A low content of formaldehyde is generallyachieved due to health concerns associated with exposure to formaldehydeemissions. If desired, conventional “formaldehyde scavengers” that areknown to react with free formaldehyde may be added to reduce the levelof formaldehyde in solution. Alternatively, the use of a silane couplingagent that is reactive with formaldehyde may also lower the freeformaldehyde content to the levels indicated above. Such silane couplingagents which reduce free formaldehyde levels include amino substitutedsilanes and their sulfonated derivatives (sulfonated amine substitutedsilanes). Low amounts of free urea are also desirable, but for differentreasons. Without being bound by theory, while free urea may itselfbecome modified by a coupling agent (e.g., it may react with asubstituted silane to improve its affinity for siliceous materials),free urea is not believed to have the requisite molecular weight, (1) infroth flotation separations, to “blind” either the gangue impurities ordesired materials (e.g., kaolin clay) to their interaction with risingair bubbles, (2) in the purification of liquid dispersions, toagglomerate a sufficiently large number of solid contaminant particlesinto flocs, or (3) in the removal of ionic species from aqueoussolutions, to bind these species to a molecule of sufficient size forretention by filtration. In particular, it has been found that resinpolymers having a number average molecular weight of greater than about100 grams/mole, and often greater than about 300 grams/mole exhibit themass needed to promote efficient separations.

Froth Flotation

When used as depressants in froth flotation separations, modified resinsof the present invention, due to their high selectivity, provide goodresults at economical addition levels. For example, the modified resinsmay be added in an amount from about 100 to about 1000 grams, andtypically from about 400 to about 600 grams, based on resin solution ordispersion weight, per metric ton of material (e.g., clay-containingore) that is to be purified by froth flotation. In general, the optimaladdition amount for a particular separation can be readily ascertainedby those of skill in the art in view of the present disclosure. Thisoptimal addition amount depends on number of factors, including the typeand amount of impurities.

Modified resins of the present invention can be applied in the frothflotation of a wide variety of value materials (e.g., minerals or metalssuch as phosphate, potash, lime, sulfate, gypsum, iron, platinum, gold,palladium, titanium, molybdenum, copper, uranium, chromium, tungsten,manganese, magnesium, lead, zinc, clay, coal, silver, graphite, nickel,bauxite, borax, borate, or high molecular weight hydrocarbons such asbitumen). Often, the raw material to be purified and recovered containssand or clay, for which the modified resin depressants described hereinare especially selective.

Although clay is often considered an impurity in conventional metal ormineral ore beneficiation, it may also be present in relatively largequantities, as the main component to be recovered. Some clays, forexample kaolin clay, are valuable minerals in a number of applications,such as mineral fillers in the manufacture of paper and rubber. Thus,one froth flotation process in which the modified resin of the presentinvention is employed involves the separation of clay from aclay-containing ore. The impurities in such ores are generally metalsand their oxides, such as iron oxide and titanium dioxide, which arepreferentially floated via froth flotation. Other impurities ofclay-containing ores include coal. Impurities originally present in mostGeorgia kaolin, which are preferentially floated in the purificationmethod of the present invention, include iron-bearing titania andvarious minerals such as mica, ilmenite, or tourmaline, which aregenerally also iron-containing.

Thus, the clay, which selectively associates with the modified resin ofthe present invention, is separately recoverable from metals, metaloxides, and coal. In the purification of clay, it is often advantageousto employ, in conjunction with the modified resin of the presentinvention as a depressant, an anionic collector such as oleic acid, aflocculant such as polyacrylamide, a clay dispersant such as a fattyacid or a rosin acid, and/or oils to control frothing.

Other representative froth flotation processes of the present inventioninvolve the beneficiation of coal, phosphate or potash, as well as othervalue metals and minerals discussed above, in which the removal ofsiliceous gangue materials such as sand and/or clay and other impuritiesis an important factor in achieving favorable process economics.Potassium ores and other ores, for example, generally comprise a mixtureof minerals in addition to sylvite (KCl), which is desirably recoveredin the froth concentrate. These include halite (NaCl), clay, andcarbonate minerals which are non-soluble in water, such as aluminumsilicates, calcite, dolomite, and anhydrite. Other ore impuritiesinclude iron oxides, titanium oxides, iron-bearing titania, mica,ilmenite, tourmaline, aluminum silicates, calcite, dolomite, anhydrite,ferromagnesian, feldspar, and debris or various other solid impuritiessuch as igneous rock and soil. In the case of coal beneficiation,non-combustible solid materials such as calcium magnesium carbonate areconsidered impurities.

One approach, particularly in the refining of clay-containing ores,involves the further modification of the base resin with an anionicfunctional group, as described in greater detail below.

The modified resin of the present invention is also advantageouslyemployed in the separation of bitumen from sand and/or clay that areco-extracted from natural oil sand deposits. Bitumen/sand mixtures thatare removed from oil or tar sands within several hundred feet of theearth's surface are generally first mixed with warm or hot water tocreate an aqueous slurry of the oil sand, having a reduced viscositythat facilitates its transport (e.g., by pipeline) to processingfacilities. Steam and/or caustic solution may also be injected tocondition the slurry for froth flotation, as well as any number of otherpurification steps, described below. Aeration of the bitumen-containingslurry, comprising sand or clay, results in the selective flotation ofthe bitumen, which allows for its recovery as a purified product. Thisaeration may be effected by merely agitating the slurry to release airbubbles and/or introducing a source of air into the bottom of theseparation cell. The optimal amount of air needed to float the desiredbitumen, without entraining excessive solid contaminants, is readilydetermined by one of ordinary skill in the art.

Thus, the use of the modified resin depressant of the present inventionadvantageously promotes the retention of the sand and/or clay impuritiesin an aqueous fraction, which is removed from the bottom section of thefroth flotation vessel. This bottoms fraction is enriched (i.e., has ahigher concentration of) the sand and/or clay impurities, relative tothe initial bitumen slurry. The overall purification of bitumen may relyon two or more stages of flotation separation. For example, the middlesection of a primary flotation separation vessel may contain asignificant amount of bitumen that can ultimately be recovered in asecondary flotation of this “middlings” fraction.

The modified resin may also benefit the froth flotation of valuematerials described herein to remove metallic contaminants and heavymetals in particular, including mercury, cadmium, lead, and arsenic aswell as compounds containing these heavy metals. The treatment of an oreslurry with the modified resin may alternatively be accompanied by,rather than froth flotation, any of the types of separations discussedbelow (e.g., filtration, cyclone separation, flotation without the useof rising air bubbles, etc.), as well as dissolved air flotation, asdiscussed below with respect to the removal of mercury from syntheticgypsum. In the case of heavy metal contaminant removal, the purificationof coal represents a specific application of increasing environmentalsignificance. Coal typically contains, for example, on the order of0.03-0.3 parts per million (ppm) of total mercury by weight, on avolatile free basis (or non-volatile basis, as described herein).Ever-tightening regulatory standards for airborne mercury emissions haveled to requirements for highly effective mercury abatement systems(e.g., activated carbon sorbent materials) on flue gas emissions fromcoal-fired power plants. The burden on such systems may therefore bereduced through the beneficiation of coal ore that is employed in powergeneration, in order to reduce the content of total mercury presenttherein. Currently, about 100 million tons of coal ore are processedusing conventional froth flotation.

Mercury may also accumulate in systems designed for reducing sulfuremissions (primarily SO₂) from coal-fired power plants. Sulfur removaland recovery, for example, is often accomplished through flue gasdesulfurization processes that involve scrubbing (or contacting) theeffluent gases from coal combustion with an aqueous alkaline solutionthat readily dissolves, reacts with, and neutralizes sulfur oxidecontaminants. Often, an economically attractive method of sulfurrecovery involves the use of aqueous calcium hydroxide (or lime) as thescrubbing medium, which reacts with sulfur oxides to form calciumsulfate, also known as synthetic gypsum. The resulting slurry ofprecipitated synthetic gypsum may be filtered to reduce its moisturecontent and further processed in conventional gypsum operations such asin the production of gypsum wallboard.

The presence of mercury in coal can therefore ultimately lead to mercurycontamination in synthetic gypsum produced via flue gas desulfurization.In particular, trace amounts of gaseous mercury in flue gas tend tocollect in alkaline scrubbing solutions. Moreover, gaseous hydrogenchloride, also normally present in flue gas, converts elemental mercuryto HgCl₂, which can adhere to the precipitated, solid synthetic gypsumparticles.

Treatment of the synthetic gypsum slurry with a depressant comprisingthe modified resin of the present invention, combined with frothflotation or other separation methods as described herein, allows for areduction in the level of mercury contamination. It is also possible toform a slurry of synthetic gypsum that has been dehydrated, for exampleusing filtration as described above, and thereafter treat this slurrywith the modified resin, in order to effectively reduce the quantity ofmercury via froth flotation. Preferably, however, the inefficienciesassociated with dehydration and subsequent rehydration are avoided bytreating the slurry prior to filtration of the synthetic gypsum andsubjecting this slurry to froth flotation. In any event, representativebeneficiation methods of the present invention comprise treating aslurry of ore comprising coal or synthetic gypsum with a depressantcomprising the modified amine-aldehyde resin of the present invention.In the case of synthetic gypsum, this material to be purified ispreferably formed, as described above, during desulfurization of fluegas from a coal-burning power plant.

Treatment of a synthetic gypsum slurry may be combined with frothflotation either during or subsequent to the treatment. Beneficiationmay alternatively involve any of the separation processes discussedherein (e.g., filtration, size or density classification, etc.). Aparticular separation process of interest in the removal of mercury fromsynthetic gypsum is known as dissolved air flotation (DAF), which may befacilitated using the modified resin. The use of DAF in the removal ofalgae and arsenic from water is described, for example, by Wert et al.,Proceedings—Water Quality Technology Conference (2003), p. 902-918.Regardless of the nature of the separation, however, the recovery and/orpurity of purified synthetic gypsum in a separation process for theremoval of mercury may be enhanced using one or more chelating agents,as discussed below, in combination with the modified resin. Chelatingagents particularly useful in the separation of mercury from syntheticgypsum will not only form a complex with mercury, but will also containa functionality that improves the ability of the complexed species toselectively report to a desired stream, such as a froth concentrate(e.g., in a froth flotation where the purified synthetic gypsum productis selectively depressed). Such functionalities include those common inconventional collectors, which aid in flotation, or those which aid insolvation or solubilization of the complexed mercury.

In a representative beneficiation process using froth flotation,treatment of the coal or synthetic gypsum feed slurry with the modifiedresin may occur before or during the froth flotation. As a result offroth flotation, purified coal or purified synthetic gypsum may beselectively recovered in either the froth concentrate or selectivelydepressed into the bottoms or tailings stream, depending on theparticular operating conditions employed. Likewise, mercury andmercury-containing compounds may be selectively floated or selectivelydepressed. Froth flotation parameters that determine which componentsare depressed or floated in a particular separation are well known tothose having skill in the art. Normally, in the froth flotation ofsynthetic gypsum, purified synthetic gypsum is selectively depressedwhile the relatively smaller amounts of mercury and other contaminantsare selected floated. Conversely, the froth flotation of coal isnormally performed such that the purified coal is selectively recoveredin the froth concentrate while mercury and other impurities areselectively recovered in the bottoms or tailings stream.

In any event, whether mercury contaminants are selectively floated ordepressed, their separation from the value mineral may be enhancedthrough the use of one or more conventional chelating agents inconjunction with the modified resin. A chelating agent may be added tothe ore slurry together with the modified resin, or alternatively beforeor after the modified resin is added. Suitable chelating agents have thecapacity to effectively bind or form a metal-ligand complex withmercury. Chelating agents may additionally improve coal beneficiation byremoving iron contaminants and iron sulfide (pyrite) in particular. Thereduction of both the iron and sulfur content of the purified coalimproves both its fuel value (through the reduction of non-combustibles)as well as its acid gas emission characteristics (through the reductionof sulfur).

Chelating agents include, for example, multi-functional carboxylatessuch as hydroxyethylenediaminetriacetic acid (HEDTA),diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraaceticacid (EDTA), diethyltriaminepentaacetic (DTPA), and nitrilotriaceticacid (NTA), which are typically used in their corresponding acetate saltforms (e.g., their sodium salt forms, such as pentasodium DTPA ortrisodium NTA). These chelating agents include, for example, those inthe Dissolvine® family of products (Akzo-Nobel Functional Chemicals bv,Netherlands), such as Dissolvine® H-40, Dissolvine® D-40, Dissolvine®D-40-L, and Dissolvine® A-150-S. Salts of oxalic acid (oxalate salts)may also be employed alone or in combination with these chelatingagents. Amino acids are also useful as agents having a carboxylic acidgroup which can chelate with iron and other metal contaminants. Whenused in conjunction with the modified resin, the amine group of an aminoacid can covalently react into the modified resin backbone, therebyproviding the modified resin with a desired chelation functionality.Suitable amino acids include arginine, cysteine, serine, alanine, etc.Likewise, agents such as caprolactam and other cyclic amides can behydrolyzed to form species having both amino and carboxylic acidfunctional groups which can similarly add chelation functionality to themodified resin.

Other classes of chelating agents include resins having sulfuratom-bearing functional groups, such as thiosemicarbazide and itsderivatives. Thiosemicarbazide may be incorporated into resins such asstyrene-divinylbenzene copolymers or ion exchange resins such as theweakly acidic Amberlite IRC-50® (Rohm and Haas Company, Philadelphia,Pa. USA). In the latter case, the resulting polymer contains amultidentate chelate ring containing O, N, and S donor sites. Arepresentative thiosemicarbazide derivative functional group isdiacetyl-bis(N-methylthiosemicarbazone).

Other sulfur-containing additives may likewise improve the efficiency(e.g., product purity and/or recovery) of froth flotation in the removalof mercury from coal or synthetic gypsum, and may therefore be employedin combination with the modified resin and optionally further incombination with one or more of the above-described chelating agents.Species having one or more mercapto functional groups, as well as one ormore acid functional groups, are effective in this application and theseinclude, for example, 2,3 dimercaptopropanesulfonate sodium (DMPS) and2,3 meso dimercaptosuccinic acid (DMSA). Other sulfur-containing speciessuch as alpha-lipoic acid, cysteine, and glutathione may also beemployed for the formation of mercury complexes, resulting in improvedsequestration of mercury in the froth flotation bottoms. Thioacidhomologues of the carboxylic acid chelating agents discussed above, aswell as their corresponding thioester derivatives, are also suitable forthis purpose. Iodine-containing derivatives of any of the chelatingagents discussed above may also be effective in the formation of stablecomplexes with mercury and other metal impurities. The effectivenessassociated with any given amount of any of the above chelating agents,sulfur-containing compounds, or other additives for any particularapplication can be readily ascertained by those having skill in the art,in view of the present disclosure. In the case of a given sulfurcontaining compound, its effectiveness will depend not only on itsaffinity for mercury contaminants in coal or synthetic gypsum, but alsoon the ease of its separation, both in its complexed and un-complexedstate, from the purified product.

Other additives which may be used in combination with the modifiedresin, to potentially improve its performance in coal ore beneficiationby froth flotation, include known reagents, collectors, frothers,promoters, and other agents used in this service, as described, forexample, by Laskowski, COAL FLOTATION AND FINE COAL UTILIZATION,Elsevier (2001).

As a result of beneficiation, the final amount of total mercury presentin the ore (e.g., comprising coal or synthetic gypsum) is less than theinitial amount (i.e., the initial amount of total mercury is reduced),on a volatile free weight basis. In representative embodiments, thefinal amount of total mercury is less than about 10 parts per billion(ppb), less than about 5 ppb, or even less than 1 ppb. The final amountof total mercury may range, for example, from about 1 to about 100 ppb,from about 1 to about 10 ppb, or from about 5 to about 50 ppb. Anyconventional method (e.g., inductively coupled plasma (ICP) or atomicabsorption spectrometry (AAS) analysis) may be used in the determinationof the total mercury amount, which refers to the amount of mercurypresent both in elemental form and in the form of mercury-containingcompounds.

In the case of coal ore used in power plants, the removal of otherimpurities, in addition to heavy metals, can significantly improve thefuel value and/or the resulting combustion emissions of the purifiedcoal recovered via froth flotation or other separation processesdiscussed herein. The reduction of nitrogen- and sulfur-containingcompounds, for example, is important in many cases for compliance withnitrogen oxide and sulfur oxide emission tolerances designed to reducethe prevalence of these acid rain precursors in the environment. Frothflotation of an impure coal ore is conventionally employed for upgradingcoal-fired power plant feedstocks in this manner. The removal ofunwanted contaminants with froth flotation may be facilitated bytreating an aqueous slurry of the impure coal ore with a modified resinof the present invention, either before or during the froth flotation.Conventional froth flotation in coal ore beneficiation is generallydescribed, for example, at http://www.cq-inc.com/Coal Primer.pdf.Purified coal recovered in the froth concentrate may have a reducedamount, relative to the impure coal, of an impurity such as nitrogen,sulfur, silicon, ash, or pyrite. The reduction in these impurities isdetermined on a volatile free basis, as described herein (e.g., on avolatile free weight basis).

The amount of nitrogen impurity refers to the total amount of nitrogenpresent in nitrogen-containing compounds in a coal sample, expressed interms of a weight fraction (or weight-%, weight-ppm, etc.) of theelement relative to the total volatile free sample weight. Otherconventional measures and analyses may also be used to compare therelative amounts of nitrogen in the impure and purified coal samples,such as measurements of the total organic nitrogen, total basicnitrogen, etc. Sulfur and silicon impurities refer to the total amountsof sulfur and silicon present either in elemental form or in compoundscontaining these elements, also generally expressed as a weight fractionon a volatile free weight basis. Silicon generally represents asignificant portion of the non-combustible ash component of coal. Assuch, beneficiation for the reduction in the amount of measured ash maysimilarly be facilitated according to methods described herein. Pyrite(or iron sulfide) is also normally measured on a volatile free weightbasis, for comparison of the amount of this impurity in the purifiedcoal relative to that in the impure coal ore. A reduction in pyritecontent of coal reduces the amount of sulfur impurity and also improvesthe fuel value (e.g., measured in BTU/lb).

Other benefits associated with the use of the modified resin in thefroth flotation of coal may therefore include an increased BTU value perunit weight, or alternatively (or in combination) a reduced amount ofmoisture. In any event, the reduced amount(s) of one or more (e.g., twoor more, or all) of the impurities described above, in the purified coalrecovered in the beneficiation, using froth flotation, of impure coalore, is/are preferably less than the corresponding reference amount(s)in a purified reference coal recovered in the same froth flotationoperation, but without using the modified resin. Preferred moisturelevels of coal that is purified according to any of the methodsdescribed herein are less than bout 12% by weight, in the range fromabout 5% to about 12% by weight, and in the range from about 5% to about10% by weight. Preferred fuel values are greater than about 12,000BTU/lb, and in the range from about 12,000 to about 13,000 BTU/lb.

Generally, in any froth flotation process according to the presentinvention, at least 70% of the value material (e.g., kaolin clay,phosphate, or bitumen) is recovered from the raw material (e.g., theclay-containing ore), with a purity of at least 85% by weight. Also,conventional known collectors may be used in conjunction with modifiedresins of the present invention, when used as depressants. Thesecollectors include, for example, fatty acids (e.g., oleic acid, sodiumoleate, hydrocarbon oils), amines (e.g., dodecylamine, octadecylamine,α-aminoarylphosphonic acid, and sodium sarcosinate), and xanthanate.Likewise, conventional depressants known in the art for a givenseparation can also be combined with the modified resin depressants. Forexample, in the case of phosphate ore froth flotation, conventionaldepressants include guar gum and other hydrocolloidal polysaccharides,sodium hexametaphosphate, etc. Conventional frothing agents that aidcollection, (e.g., methylisobutylcarbinol, pine oil, and polypropyleneoxides) may also be used, in accordance with normal flotation practice,in conjunction with the modified resin depressants of the presentinvention.

In froth flotation separations, the pH of the slurry to which themodified resins of the present invention, when used as depressants, areadded will vary according to the particular material to be processed, asis appreciated by those skilled in the art. Commonly, the pH valuesrange from neutral (pH 7) to strongly alkaline (e.g., pH 12). It isrecognized that in some flotation systems, for example in copper sulfideflotations, high pH values (e.g., from about 8 to about 12.5) give bestresults.

Typically in froth flotation for the beneficiation of solid materialssuch as mineral or metal ores, the raw materials are usually firstground to the “liberation mesh” size where most of the valuematerial-containing particles are either separate mineral or metalparticles or salt crystals, and the gangue (e.g., clay and/or sand) ismixed between these particles. The solid material may be ground toproduce, for example, one-eighth inch average diameter particles priorto incorporation of the material into a brine solution to yield anaqueous slurry. After crushing and slurrying the material, the slurrymay be agitated or stirred in a “scrubbing” process that breaks downclay or ash into very fine particles that remain in the brine as a muddysuspension. Some of this clay or ash may be washed off the oreparticles, into a clay-containing aqueous suspension or brine, prior tofroth flotation. Also, as is known in the art, any conventional sizeclassification operations, some of which are discussed in greater detailbelow, may be employed to further reduce/classify raw material particlesize, remove clay- or ash-containing brine, and/or recover smaller solidparticles from the muddy brine, prior to froth flotation. Such sizeclassification operations include further crushing/screening, cycloning,and/or hydro separation, any of which may be performed with or withoutthe use of a modified resin.

Ore beneficiation according to the present invention comprises treatingan aqueous slurry of the ore with a depressant comprising a modifiedresin, as described herein. The treatment of the ore slurry with thedepressant typically involves combining the depressant and slurry (e.g.,by adding the depressant to the slurry), normally in a manner such thatthe depressant is readily dispersed throughout. The treatment may occurbefore or during froth flotation, or before or during any of the otherseparation processes described herein (e.g., filtration, cycloneseparation, dissolved air flotation, etc.). In the case of treatmentbefore froth flotation, the treatment may also comprise conditioning theore in the presence of the depressant, prior to froth flotation.Conditioning may be beneficial in allowing the depressant and ore slurryto thoroughly mix for a given time period, typically from about 30seconds to about 10 minutes, prior to subjecting the mixture to aerationor froth flotation. During the conditioning time, the depressant canbecome associated, for example, with unwanted gangue material, therebyimproving the performance of the subsequent froth flotation.Conditioning of a depressant/slurry mixture in the absence of aerationor froth flotation can occur in a separate conditioning vessel such as amixer or mechanical flotation cell, pipe, barrel, etc. prior to transferof the mixture to a froth flotation cell. Alternatively, conditioningcan occur in the same vessel used for froth flotation. The same ordifferent conditions in terms of temperature, pH, agitation, etc., maybe used for conditioning and froth flotation. Typical conditions thatmay be employed in a conditioning step include a temperature from about1° C. to about 95° C. and a pH of at least about 2.0, and often a pHfrom about 3.0 to about 7.0. Also, the same agents, as conventionallyused and/or discussed herein, may be incorporated into the ore slurry ina conditioning step, in addition to the depressant. Such agents includecollectors, activators, frothing agents, pH modifiers, etc.

In froth flotation, the slurry, typically having a solids content fromabout 5% to about 50% by weight, is transferred to one or more frothflotation cells. Air is forced through the bottoms of these cells and arelatively hydrophobic fraction of the material, having a selectiveaffinity for the rising bubbles, floats to the surface (i.e., thefroth), where it is skimmed off and recovered in the froth concentrate.A bottoms product that is hydrophilic relative to the froth concentratemay also be recovered. The process may be accompanied by agitation.Commercially salable products can be prepared from the separatefractions recovered in this manner, often after further conventionalsteps, including further separation (e.g., by centrifuge), drying (e.g.,in a gas fired kiln), size classification (e.g., screening), andrefining (e.g., crystallization), are employed.

The froth flotation of the present invention may, though not always,involve flotation in “rougher cells” followed by one or more “cleanings”of the rougher concentrate. Two or more flotation steps may also beemployed to first recover a bulk value material comprising more than onecomponent, followed by a selective flotation to separate thesecomponents. Modified resins of the present invention, when used asdepressants, can be used to advantage in any of these steps to improvethe selective recovery of desired materials via froth flotation. Whenmultiple stages of froth flotation are used, the modified resins may beadded using a single addition prior to multiple flotations or they maybe added separately at each flotation stage.

Other Separations

Because of their affinity for solid contaminants in liquid suspensions,the modified resins of the present invention are applicable in a widevariety of separations, and especially those involving the removal ofsiliceous contaminants such as sand, clay, and/or ash from aqueousliquid suspensions or slurries of these contaminants. Such aqueoussuspensions or slurries may therefore be treated with modified resins ofthe present invention, allowing for the effective separation of at leasta portion of the contaminants, in a contaminant-rich fraction, from apurified liquid. A “contaminant-rich” fraction refers to a part of theliquid suspension or slurry that is enriched in solid contaminants(i.e., contains a higher percentage of solid contaminants thanoriginally present in the liquid suspension or slurry). Conversely, thepurified liquid has a lower percentage of solid contaminants thanoriginally present in the liquid suspension or slurry.

The separation processes described herein are applicable to“suspensions” as well as to “slurries” of solid particles. These termsare sometimes defined equivalently and sometimes are distinguished basedon the need for the input of at least some agitation or energy tomaintain homogeneity in the case of a “slurry.” Because the methods ofthe present invention, described herein, are applicable broadly to theseparation of solid particles from aqueous media, the term “suspension”is interchangeable with “slurry” (and vice versa) in the presentspecification and appended claims.

The treatment step may involve adding a sufficient amount of themodified resin to electronically interact with and either coagulate orflocculate the solid contaminants into larger agglomerates. Thenecessary amount can be readily determined depending on a number ofvariables (e.g., the type and concentration of contaminant), as isreadily appreciated by those having skill in the art. In otherembodiments, the treatment may involve contacting the liquid suspensioncontinuously with a fixed bed of the modified resin, in solid form.

During or after the treatment of a liquid suspension with the modifiedresin, the coagulated or flocculated solid contaminant (which may nowbe, for example, in the form of larger, agglomerated particles or flocs)is removed. Removal may be effected by flotation (with or without theuse of rising air bubbles as described previously with respect to frothflotation) or sedimentation. The optimal approach for removal willdepend on the relative density of the flocs and other factors.Increasing the quantity of modified resin that is used to treat thesuspension can in some cases increase the tendency of the flocs to floatrather than settle. Filtration or straining may also be an effectivemeans of removing the agglomerated flocs of solid particulates,regardless of whether they reside predominantly in a surface layer or ina sediment.

Examples of liquid suspensions that may be purified according to thepresent invention include oil and gas well drilling fluids, whichaccumulate solid particles of rock (or drill cuttings) in the normalcourse of their use. These drilling fluids (often referred to as“drilling muds”) are important in the drilling process for severalreasons, including transporting these drill cuttings from the drillingarea to the surface, where their removal allows the drilling mud to berecirculated. The addition of modified resins of the present inventionto oil well drilling fluids, and especially water-based (i.e., aqueous)drilling fluids, effectively coagulates or flocculates solid particlecontaminants into larger clumps (or flocs), thereby facilitating theirseparation by settling or flotation. The modified resins of the presentinvention may be used in conjunction with known flocculants for thisapplication such as polyacrylamides or hydrocolloidal polysaccharides.Generally, in the case of suspensions of water-based oil or gas welldrilling fluids, the separation of the solid contaminants is sufficientto provide a purified drilling fluid for reuse in drilling operations.

Other aqueous suspensions of practical interest include theclay-containing aqueous suspensions or brines, which accompany orerefinement processes, including those described above. The production ofpurified phosphate from mined calcium phosphate rock, for example,generally relies on multiple separations of solid particulates fromaqueous media, whereby such separations can be improved using themodified resin of the present invention. In the overall process, calciumphosphate is mined from deposits at an average depth of about 25 feetbelow ground level. The phosphate rock is initially recovered in amatrix containing sand and clay impurities. The matrix is first mixedwith water to form a slurry, which, typically after mechanicalagitation, is screened to retain phosphate pebbles and to allow fineclay particles to pass through as a clay slurry effluent with largeamounts of water.

These clay-containing effluents generally have high flow rates andtypically carry less than 10% solids by weight and more often containonly from about 1% to about 5% solids by weight. The dewatering (e.g.,by settling or filtration) of this waste clay, which allows for recycleof the water, poses a significant challenge for reclamation. The timerequired to dewater the clay, however, can be decreased throughtreatment of the clay slurry effluent, obtained in the production ofphosphate, with the modified resin of the present invention. Reductionin the clay settling time allows for efficient re-use of the purifiedwater, obtained from clay dewatering, in the phosphate productionoperation. In one embodiment of the purification method, wherein theliquid suspension is a clay-containing effluent slurry from a phosphateproduction facility, the purified liquid contains less than about 1%solids by weight after a settling or dewatering time of less than about1 month.

In addition to the phosphate pebbles that are retained by screening andthe clay slurry effluent described above, a mixture of sand and finerparticles of phosphate is also obtained in the initial processing of themined phosphate matrix. The sand and phosphate in this stream areseparated by froth flotation which, as described earlier, can beimproved using the modified resin of the present invention as adepressant for the sand.

In the area of slurry dewatering, another specific application of themodified resin is in the filtration of coal from water-containingslurries. The dewatering of coal is important commercially, since theBTU value per unit weight and hence the quality of the coal decreaseswith increasing water content. In one embodiment of the invention,therefore, the modified resin is used to treat an aqueouscoal-containing suspension or slurry prior to dewatering the coal byfiltration.

As used herein, “beneficiation” broadly refers to any process forpurifying and/or upgrading a value material as described herein. In thecase of coal ore purification, a number of beneficiation operations areconventionally used in an effort to improve the quality of coal that isburned, for example, in electricity-generating power plants. Asdiscussed previously, for example, such quality improvement processesaddress environmental concerns that have resulted in lower tolerancesfor metallic contaminants such as mercury and arsenic, as well asnitrogen- and sulfur-containing compounds that lead to acid rain. Frothflotation, as discussed previously, affords one method for thepurification of a coal ore via treatment of an aqueous slurry of the orewith the modified resin of the present invention. Treatment canalternatively occur prior to or during conventional coal size or densityclassification operations to facilitate the reduction in the amount(s)of one or more of the mercury, nitrogen, sulfur, silicon, ash, andpyrite impurities in the purified coal, wherein these impurities aremeasured on a volatile free weight basis and as described previously.The modified amine-aldehyde resin can also be used in conjunction withsize or density classification operations to reduce moisture and/orincrease the fuel value of the purified coal (e.g., measured in BTU/lb).Preferably, the reduction of the amount(s) of one or more (e.g., two ormore, or all) of the impurities described above, in the purified coalrecovered in the size or density classification operation is/arepreferably less than the corresponding reference amount(s) in a purifiedreference coal recovered in the same size or density classificationoperation, but without using the modified amine-aldehyde resin.

In general, the reduction of one of the impurities noted above in thepurified coal, results in a corresponding reduction in the amount of oneor more other undesired impurities. For example, a reduction in pyritegenerally leads to a reduction in mercury and other inorganic materialssuch as silicon-containing ash. In one embodiment, the use of one ormore size or density classification operations in conjunction with themodified amine-aldehyde resin results in a reduction in amounts of allthe impurities noted above.

Suitable conventional size or density classification operations includecyclone separation, heavy medium (or heavy media or dense medium)separation, filtration, and screening, any of which may be used incombination (e.g., serially or in parallel) with each other or withfroth flotation. Generally, these operations precede froth flotation toprovide, in combination with froth flotation, an upgraded or purifiedcoal meeting the various specifications (e.g., nitrogen and sulfurlevels) required for combustion in electricity-generating power plants.For example, water-only or clarifying cyclone operations process a feedstream of a raw coal ore slurry, which is fed tangentially underpressure into a cyclone. Centrifugal force moves heavier material to thecyclone wall, where it is subsequently typically transported to theunderflow at the apex (or spigot). Lighter coal particles that aredisposed toward the center of the cyclone are removed via a pipe (orvortex finder) to the overflow. The targeted density at which light andheavy particles are separated may be adjusted by varying pressure,vortex finder length, and/or apex diameter. Such water-only orclarifying cyclones typically treat material in the 0.5-1 mm size rangeand may involve two ore more stages of separation to improve separationefficiency.

Heavy medium separation uses a dense liquid medium (e.g., magnetite at aspecified magnetite/water ratio) to float particles (e.g., coal) havinga density below that of the medium and depress particles (e.g., sand orrock) having a density above that of the medium. Heavy medium separationmay be employed in a simple deep or shallow “bath” configuration or maybe included as part of a cyclone separation operation to enhance thegravitational separation forces with centrifugal forces. Often, one ormore stages of a clarifying cyclone separation operation are followed byone or more stages of heavy medium cyclone separation and one ore morescreening steps to yield an appropriately sized and purified (e.g., apre-conditioned or pre-treated) coal feedstock for subsequent frothflotation.

Another significant application of the modified resin of the presentinvention is in the area of sewage treatment, accompanied by variousprocesses that are undertaken to remove contaminants from industrial andmunicipal waste water. Such processes thereby purify sewage to provideboth purified water that is suitable for disposal into the environment(e.g., rivers, streams, and oceans) as well as a sludge. Sewage refersto any type of water-containing wastes which are normally collected insewer systems and conveyed to treatment facilities. Sewage thereforeincludes municipal wastes from toilets (sometimes referred to as “foulwaste”) and basins, baths, showers, and kitchens (sometimes referred toas “sullage water”). Sewage also includes industrial and commercialwaste water, (sometimes referred to as “trade waste”), as well asstormwater runoff from hard-standing areas such as roofs and streets.

Conventional processes for purifying sewage often involve preliminary,primary, and secondary steps. Preliminary steps often include thefiltration or screening of large solids such as wood, paper, rags, etc.,as well as coarse sand and grit, which would normally damage pumps.Subsequent primary steps are then employed to separate most of theremaining solids by settling in large tanks, where a solids-rich sludgeis recovered from the bottom of these tanks and processed further. Apurified water is also recovered and normally subjected to secondarysteps involving biological processes.

Thus, in one embodiment of the present invention, the purification ofsewage water by settling or sedimentation may comprise treating thesewage water, before or during the settling or sedimentation operation,with the modified resin of the present invention. This treatment may beused to improve settling operation (either batch or continuous), forexample, by decreasing the residence time required to effect a givenseparation (e.g., based on the purity of the purified water and/or thepercent recovery of solids in the sludge). Otherwise, the improvementmay be manifested in the generation of a higher purity of the purifiedwater and/or a higher recovery of solids in the sludge, for a givensettling time.

After treatment of sewage with the modified resin of the presentinvention and removing a purified water stream by sedimentation, it isalso possible for the modified resin to be subsequently used for, orintroduced into, secondary steps as described above to further purifythe water. These secondary operations normally rely on the action ofnaturally occurring microorganisms to break down organic material. Inparticular, aerobic biological processes substantially degrade thebiological content of the purified water recovered from primary steps.The microorganisms (e.g., bacteria and protozoa) consume biodegradablesoluble organic contaminants (e.g., sugars, fats, and other organicmolecules) and bind much of the less soluble fractions into flocs,thereby further facilitating the removal of organic material.

Secondary processes rely on “feeding” the aerobic microorganisms oxygenand other nutrients which allow them to survive and consume organiccontaminants. Advantageously, the modified resin of the presentinvention, which contains nitrogen, can serve as a “food” source formicroorganisms involved such secondary processing steps, as well aspotentially an additional flocculant for organic materials. In oneembodiment of the invention, therefore, the sewage purification methodfurther comprises, after removing purified water (in the primarytreatment step) by sedimentation, further processing the purified waterin the presence of microorganisms and the modified resin, and optionallywith an additional amount of modified resin, to reduce the biochemicaloxygen demand (BOD) of the purified water. As is understood in the art,the BOD is an important measure of water quality and represents theoxygen needed, in mg/l (or ppm by weight) by microorganisms to oxidizeorganic impurities over 5 days. The BOD of the purified water aftertreatment with microorganisms and the modified resin, is generally lessthan 10 ppm, typically less than 5 ppm, and often less than 1 ppm.

The modified resin of the present invention may also be applied to thepurification of pulp and paper mill effluents. These aqueous wastestreams normally contain solid contaminants in the form of cellulosicmaterials (e.g., waste paper; bark or other wood elements, such as woodflakes, wood strands, wood fibers, or wood particles; or plant fiberssuch as wheat straw fibers, rice fibers, switchgrass fibers, soybeanstalk fibers, bagasse fibers, or cornstalk fibers; and mixtures of thesecontaminants). In accordance with the method of the present invention,the effluent stream comprising a cellulosic solid contaminant is treatedwith the modified resin of the present invention, such that purifiedwater may be removed via sedimentation, flotation, or filtration.

In the separation of bitumen from sand and/or clay impurities asdescribed previously, various separation steps may be employed eitherbefore or after froth flotation of the bitumen-containing slurry. Thesesteps can include screening, filtration, and sedimentation, any of whichmay benefit from treatment of the oil sand slurry with the modifiedresin of the present invention, followed by removal of a portion of thesand and/or clay contaminants in a contaminant-rich fraction (e.g., abottoms fraction) or by removal of a purified bitumen fraction. Asdescribed above with respect to phosphate ore processing watereffluents, which generally contain solid clay particles, the treatingstep can comprise flocculating these contaminants to facilitate theirremoval (e.g., by filtration). Waste water effluents from bitumenprocessing facilities will likewise contain sand and/or clay impuritiesand therefore benefit from treatment with the modified resin of thepresent invention to dewater them and/or remove at least a portion ofthese solid impurities in a contaminant-rich faction. A particularprocess stream of interest that is generated during bitumen extractionis known as the “mature fine tails,” which is an aqueous suspension offine solid particulates that can benefit from dewatering. Generally, inthe case of sand and/or clay containing suspensions from a bitumenproduction facility, separation of the solid contaminants is sufficientto allow the recovery or removal of a purified liquid or water streamthat can be recycled to the bitumen process.

The treatment of various intermediate streams and effluents in bitumenproduction processes with the modified resin of the present invention isnot limited only to those process streams that are at least partlysubjected to froth flotation. As is readily appreciated by those ofskill in the art, other techniques (e.g., centrifugation via the“Syncrude Process”) for bitumen purification will generate aqueousintermediate and byproduct streams from which solid contaminant removalis desirable.

The modified resins of the present invention can be employed in theremoval of suspended solid particulates, such as sand and clay, in thepurification of water, and particularly for the purpose of rendering itpotable. Moreover, modified resins of the present invention have theadditional ability to complex metallic cations (e.g., lead and mercurycations) allowing these unwanted contaminants to be removed inconjunction with solid particulates. Therefore, modified resins of thepresent invention can be used to effectively treat impure water havingboth solid particulate contaminants as well as metallic cationcontaminants. Without being bound by theory, it is believed thatelectronegative moieties, such as the carbonyl oxygen atom on theurea-formaldehyde resin polymer backbone, complex with undesired cationsto facilitate their removal. Generally, this complexation occurs at a pHof the water that is greater than about 5 and typically in the rangefrom about 7 to about 9.

Another possible mechanism for the removal of metallic cations is basedon their association with negatively charged solid particulates.Flocculation and removal of these particulates will therefore alsocause, at least to some extent, the removal of metallic cations.Regardless of the mechanism, in one embodiment, the treatment andremoval of both of these contaminants can be carried out according tothe present invention to yield potable water.

The removal of metallic cations may represent the predominant or eventhe sole means of water purification that is effected by the modifiedresin, for example when the water to be purified contains little or nosolid particulates. Solid forms of the modified resin may be used toremove cations in a continuous process whereby the impure watercontaining metallic cations is continuously passed through a fixed bedof the resin. Alternatively, soluble forms of the modified resin,generally having a lower molecular weight, may be added to the impurewater in order to treat it. The complexed cations in this case can beremoved, for example, by ultrafiltration through a porous membrane(e.g., polysulfone) having a molecular weight cutoff that is less thanthe molecular weight of the modified resin. The water purificationmethods described herein may also be used in conjunction with knownmethods including reverse osmosis, UV irradiation, etc.

To increase the effectiveness of the modified resins in complexing withmetallic cations, it may be desirable to further modify the base resinas described above with one or more anionic functional groups. Suchmodifications are known in the art and can involve the reaction of thebase resin or modified resin to incorporate the desired functional group(e.g., by sulfonation with sodium metabisulfite). Alternatively, thefurther modification is achieved during preparation of the base resin(e.g., during condensation) by incorporating an anionic co-monomer, suchas sodium acrylate, either into the base resin or into the couplingagent. For example, as described above, organopolysiloxane derivativesused as coupling agents may be prepared by incorporating further organicresin functionalities, such as acrylate, into the coupling agent.Representative additional functionalities with which the base resin ormodified resin, including a urea-formaldehyde resin, may be modifiedinclude the anionic functional groups bisulfite, acrylate, acetate,carbonate, azide, amide, etc. Procedures for modifying the base resinwith additional functionalities are known to those having skill in theart. The incorporation of anionic functional groups into the base resinmay also be employed in separations involving the purification ofslurries containing solid clay particles (e.g., by froth flotation,flocculation, etc.), including those described above, such as in thepurification of kaolin clay ore. Without being bound by theory,sulfonation of the base resin or the incorporation of other anionicfunctional groups can also increase hydrogen bonding between the baseresin and the surrounding aqueous phase to inhibit condensation of thebase resin or otherwise improve its stability.

As described above, therefore, the present invention, in one embodiment,is a method for purifying water containing a metallic cation by treatingthe water with a modified resin as described herein and which may befurther modified with an anionic group. Removal of at least a portion ofthe metallic cations may be effected by retaining them on a fixed bed ofthe modified resin or otherwise by filtering them out. In the lattercase, removal by filtration such as membrane filtration is made possibleby the association of the metallic cations either directly with themodified resin or indirectly with the modified resin via solidparticulates, for which the modified resin has affinity. In the case ofindirect association, as described earlier, flocculation of the solidparticulates will also necessarily agglomerate at least a portion of themetallic cations, which may therefore be removed by flotation orsedimentation of these particulates.

The modified resin of the present invention is therefore advantageouslyused to treat water for the removal of metallic cations such as arsenic,lead, cadmium, copper, and mercury that are known to pose health riskswhen ingested. These cations thus include As⁺⁵, Pb⁺², Cd⁺², Cu⁺², Hg⁺²,Zn⁺², Fe⁺², and mixtures thereof. Generally, a degree of removal iseffected such that the purified water is essentially free of one or moreof the above metallic cations. By “essentially free” is meant that theconcentration(s) of one or more metallic cation(s) of interest is/arereduced to concentration(s) at or below those considered safe (e.g., bya regulatory agency such as the U.S. Environmental Protection Agency).Therefore, in various representative embodiments, the purified waterwill contain at most about 10 ppb of As⁺⁵, at most about 15 ppb of Pb⁺²,at most about 5 ppb of Cd⁺², at most about 1.3 ppm of Cu⁺², and/or atmost about 2 ppb of Hg⁺². That is, generally at least one, typically atleast two, and often all, of the above-mentioned cations are at or belowthese threshold concentration levels in the purified water.

In any of the applications described herein, it is possible to stabilizethe modified resin of the present invention by reaction with an alcohol(i.e., etherification). Without being bound by theory, it is believedthat etherification of pendant alkylol functionalities can inhibitfurther condensation of the base resin (e.g., condensation of aurea-formaldehyde resin with itself). This can ultimately hinder orprevent the precipitation of the base resin during long term storage,such that, relative to their corresponding non-etherified resins, theetherified resins can have increased molecular weight without anaccompanying loss in stability

Etherification thus involves reacting the amine-aldehyde adducts orcondensates, or even the modified resins, as described above, with analcohol. In one embodiment, a urea-formaldehyde base resin is etherifiedwith an alcohol having from 1 to 8 carbon atoms, prior its modificationwith a coupling agent. Representative alcohols for use in theetherification include methanol (e.g., to effect methylation), ethanol,n-propanol, isopropanol, n-butanol, and isobutanol. In exemplarypreparations of etherified base resins, the amine-aldehyde adduct orcondensate reaction product is heated to a temperature from about 70° C.to about 120° C. in the presence of an alcohol until the etherificationis complete. An acid such as sulfuric acid, phosphoric acid, formicacid, acetic acid, nitric acid, alum, iron chloride, and other acids maybe added before or during the reaction with alcohol. Often, sulfuricacid or phosphoric acid is employed.

All references cited in this specification, including withoutlimitation, all U.S., international, and foreign patents and patentapplications, as well as all abstracts, papers (e.g., journal articles,periodicals, etc.), and Internet postings, are hereby incorporated byreference into this specification in their entireties. The discussion ofthe references herein is intended merely to summarize the assertionsmade by their authors and no admission is made that any referenceconstitutes prior art. Applicants reserve the right to challenge theaccuracy and pertinence of the cited references. In view of the above,it will be seen that several advantages of the invention are achievedand other advantageous results obtained.

As various changes could be made in the above methods and compositionswithout departing from the scope of the invention, it is intended thatall matter contained in this application, including all theoreticalmechanisms and/or modes of interaction described above, shall beinterpreted as illustrative only and not limiting in any way the scopeof the appended claims.

The following examples are set forth as representative of the presentinvention. These examples are not to be construed as limiting the scopeof the invention as these and other equivalent embodiments will beapparent in view of the present disclosure and appended claims.

Froth Flotation

EXAMPLE 1

Various urea-formaldehyde resins were prepared as low molecular weightcondensate resins, initially under alkaline conditions to formmethylolated urea adducts, and then under acidic conditions to form thecondensate. The condensation reaction was stopped by raising the pH ofthe condensation reaction mixture. Other preparation conditions were asdescribed above. These base resins are identified in Table 1 below withrespect to their molecular weight (Mol. Wt.) in grams/mole and theirapproximate normalized weight percentages of free urea, cyclic ureaspecies (cyclic urea), mono-methylolated urea (Mono), and combineddi-/tri-methylolated urea (Di/Tri). In each case, the base resins werein a solution having a resin solids content of 45-70%, a viscosity of500 cps or less, and a free formaldehyde content of less than 5% byweight.

TABLE 1 Urea-Formaldehyde Base Resins ID Mol. Wt.^(a) Free Urea CyclicUrea Mono Di/Tri Resin A 406 8 39 30 23 Resin B* 997 5 50 22 23 Resin Cand C′** 500 6 46 25 23 Resin D and 131 43 21 30 6 D′*** Resin E 578 018 10 72 Resin F 1158 1 44 11 44 Resin G 619 0 26 3 71 *Resin B is avery stable urea-formaldehyde resin, having a high cyclic urea content.This resin is described in U.S. Pat. No. 6,114,491. **Resin C′ wasformed by adding, in addition to Silane #1 (described below), 2% byweight of diethylenetriamine and 2% by weight dicyandiamide to themixture of urea and formaldehyde during resin preparation. ***Resin D′was formed by adding 0.75% by weight cyclic phosphate ester to themixture of urea and formaldehyde during resin preparation. The resin wasa low molecular weight formulation with a high content of free urea,essentially no free formaldehyde, and a high content of non-volatiles(about 70% solids). ^(a)Number average molecular weight determined usinggel permeation chromatography (GPC) with appropriately sized PLgel ™columns (Polymer Laboratories, Inc., Amherst, MA, USA), 0.5% glacialacetic acid/tetrahydrofuran mobile phase at 1500 psi, and polystyrene,phenol, and bisphenol-A calibration standards.

The urea-formaldehyde resin solutions described above were modified bysilane coupling agents, in order to prepare resin depressants of thepresent invention. Silane coupling agents #1, #2, or #3, all substitutedsilanes as identified in Table 2 below, were used in these modifiedresin preparations.

TABLE 2 Silane Coupling Agents ID Type Source Silane #1Ureidopropyltrimethoxysilane Silane A1160^(†) Silane #2 Oligomericaminoalkylsilane Silane A1106^(†) Silane #3 AminopropyltriethoxysilaneSilane A1100^(†) ^(†)Available under the trade name Silquest (GESilicones-OSi Specialties, Wilton, CT, USA)

EXAMPLE 2

The above urea-formaldehyde base resins described in Table 1 weremodified by the silane coupling agents #1, #2, and #3, as described inTable 2, according to procedures described previously. Namely, thesilane coupling agent was added to the base resin solution in an amountof about 0.1-2.5% based on the weight of the resin solution, afterformation of a low molecular weight condensate and the subsequentaddition of a base to increase the solution pH and halt the condensationreactions, as described above. The alkaline mixture of the base resinand silane coupling agent was then heated to a temperature of about35-45° C. for about 0.5-4 hours, until a viscosity of about 350-450 cpswas achieved.

EXAMPLE 3

Various urea-formaldehyde resin samples, representing both unmodifiedresins or resins modified with silane coupling agents as noted above,along with a control depressant, were tested for their selectivity inremoving siliceous sand and clay impurities from potash ore by frothflotation, in a laboratory-scale beneficiation study. In each test, theamount of depressant employed per unit weight of ore to be beneficiated,the solids content of the ore slurry, the pH of the slurry, thevolumetric air flow rate per unit volume of the slurry, the phosphatepurity of the ore prior to beneficiation, and other conditions wererepresentative of a commercial operation. In each test, the orerecovered by flotation was at least 90% by weight pure phosphatematerial. A commercially available guar gum was used as a depressantcontrol sample.

In these experiments, the performance of each depressant was measuredbased on the quantity of potash that could be recovered (i.e., floated)at a specified purity. This quantity provided the measure of eachdepressant's selectively in binding to unwanted gangue materials. Inother words, the higher the selectivity of a depressant, the greater thequantity of 90% pure phosphate that could be floated. The following datawere obtained, as shown in Table 3 below.

TABLE 3 Performance of Depressants in Phosphate Recovery DepressantGrams of >90% Potassium Floated Control 1-Guar Gum 212 Resin A, Modifiedby Silane #1 230 Resin A, Unmodified  85 Resin B, Modified by Silane #1226 Resin B, Unmodified  97 Resin C, Modified by Silane #1 172 Resin C′,Modified by Silane #1 158 Resin D, Modified by Silane #1  82 (avg. of 2tests) Resin D′, Unmodified 100 Resin E, Modified by Silane #1 215 ResinE, Modified by Silane #2 232 (avg. of 2 tests) Resin E, Modified bySilane #3 226 (avg. of 2 tests) Resin F, Modified by Silane #1 229 ResinF, Modified by Silane #2 231 Resin F, Modified by Silane #3 225 Resin G,Modified by Silane #1 223 Resin G, Modified by Silane #2 228 Resin G,Modified by Silane #3 224

Based on the above results, the use of a silane coupling agent to modifya urea-formaldehyde base resin, preferably via a covalent link, candramatically improve the resin performance as a depressant in frothflotation. Also, the performance advantage associated with the use of asilane coupling agent becomes more evident as the molecular weight ofthe base resin is increased. Especially good performance is obtained forbase resins having a molecular weight above about 300 grams/mole, beforemodification. This is illustrated in FIG. 1, showing the performance ofsilane coupling agent-modified resins compared to unmodified resins, forresins having a molecular weight from about 400 to about 1200grams/mole. Moreover, the performance of urea-formaldehyde resins withinthis molecular weight range is not appreciably affected by the use ofadditional resin modifiers (e.g., diethylenetriamine, dicyandiamide,phosphate esters, etc.) of the base resin.

FIG. 1 also illustrates that silane coupling agent-modified resinshaving a molecular weight from about 400 to about 1200 grams/moleperform superior to their unmodified counterpart and generally performsuperior to guar gum, which is known in the art to bind clay and talc,but is considerably more expensive. Furthermore, in contrast to guargun, the depressants of the present invention showed substantiallyhigher selectivity for the flotation of coarse phosphate particles. Thecomparatively greater amount of fines material in the purified phosphatethat was floated in the test with guar gum would add significantly tothe expense associated with downstream drying and screening operationsto yield a salable product.

EXAMPLE 4

A sample of a modified resin depressant of the present invention wastested for its performance in a potash beneficiation plant using frothflotation, relative to guar gum, which is currently employed at theplant as a commercial depressant of gangue materials. The depressant ofthe present invention used for this test was Resin F, Modified by Silane#2, as described in Examples 1-3 above.

For the comparative tests, the amount of depressant employed per unitweight of ore to be beneficiated, the solids content of the ore slurry,the pH of the slurry, the volumetric air flow rate per unit volume ofthe slurry, the potassium mineral purity of the ore prior tobeneficiation, and other conditions were representative of a commercialoperation. The performance of each depressant was measured based on thequantity of phosphate that could be recovered (i.e., floated) at aspecified purity. This quantity provided the measure of eachdepressant's selectively in binding to unwanted gangue materials. Inother words, the higher the selectivity of a depressant, the greater thequantity of potash that could be floated at a specified purity.

Relative to guar gum, the depressant of the present invention providedan increase in the yield of purified potash of about 19%. Furthermore,the yield of coarse particles of the desired potash (potassium chloride)mineral was substantially higher using the urea-formaldehyde resin,modified with a silane coupling agent. For the reasons explained above,this improvement in the yield of coarse material reduces costsassociated with drier energy requirements and other downstreamoperations, as well as the overall processing time needed for furtherrefinement, prior to sale.

EXAMPLE 5

Additional urea-formaldehyde resins were prepared as condensate resinsas described in Example 1, but with generally higher molecular weights.These base resins are identified in Table 4 below with respect to theirformaldehyde : urea (F:U) molar ratio, molecular weight (Mol. Wt.) ingrams/mole and their approximate normalized weight percentages of freeurea, cyclic urea species (cyclic urea), mono-methylolated urea (Mono),and combined di-/tri-methylolated urea (Di/Tri).

TABLE 4 Urea-Formaldehyde Base Resins Mol. ID F:U (molar) Wt. Free UreaCyclic Urea Mono Di/Tri Resin H 2.73 3916 1 39 8 52 Resin I 2.15 1941 147 14 38 Resin J 1.97 1078 4 39 22 35 Resin K 1.86 503 7 25 28 40 ResinL 1.87 334 7 26 30 37

EXAMPLE 6

The above urea-formaldehyde base resins described in Table 4 weremodified by the substituted silane coupling agent #3(aminopropyltriethoxysilane, Silane A1100, available under the tradename Silquest (GE Silicones-OSi Specialties, Wilton, Conn., USA)), asdescribed above in Table 2. The modification of these base resins wasperformed according to procedures described above in Example 2.

EXAMPLE 7

The modified urea-formaldehyde resin samples prepared in Example 6 weretested for their performance in a potash beneficiation plant, in whichsiliceous sand and clay impurities were removed from potash ore by frothflotation. The ore recovered (i.e., floated), as at least 90% by weightpure phosphate material, was calculated for each of the depressantsprepared in Example 6, at both 1 lb/ton and 2 lb/ton depressant/raw oredosage levels. This recovery was expressed as the weight percent of thetheoretical yield. In each test, the solids content of the ore slurry,the pH of the slurry, the volumetric air flow rate per unit volume ofthe slurry, the phosphate purity of the ore prior to beneficiation, andother conditions were representative of a commercial operation. Thefollowing data were obtained, as shown in Table 5 below.

TABLE 5 Performance of Depressants in Phosphate Recovery PercentRecovery of >90% Pure Potassium Depressant 1 lb/ton dosage 2 lb/tondosage Resin H, Modified by Silane #3 30.60 33.56 Resin I, Modified bySilane #3 18.24 21.05 Resin J, Modified by Silane #3 23.84 27.08 ResinK, Modified by Silane #3 24.75 27.33 Resin L, Modified by Silane #326.11 31.28 Resin L, Modified by Silane #3 27.35 33.86

Based on the above results, the use of a silane coupling agent to modifya urea-formaldehyde base resin, preferably via a covalent link, providesdepressants having good performance in ore benefication via frothflotation. The use of such depressants has been confirmed forurea-formaldehyde base resins having number average molecular weights ofup to about 4000 g/mole.

EXAMPLE 8

A urea-formaldehyde (UF) resin, modified with a silane coupling agent asdescribed above, was tested for its ability to reduce the dewateringtime, by filtration, of various solid contaminants suspended in aqueousslurries. In each experiment, a 25 gram sample of solid contaminant wasuniformly slurried with 100 grams of 0.01 molar KNO₃. The pH of theslurry was measured. The slurry was then subjected to vacuum filtrationusing a standard 12.7 cm diameter Buchner funnel apparatus and 11.0 cmdiameter Whatman qualitative #1 filter paper. The dewatering time ineach case was the time required to recover 100 ml of filtrate throughthe filter paper.

For each solid contaminant tested, a control experiment was run,followed by an identical experiment, differing only in (1) the additionof 0.5-1 grams of silane modified UF resin to the slurry and (2) mixingof the slurry for one additional minute, after a uniform slurry wasobtained upon stirring. Results are shown below in Table 6.

TABLE 6 Dewatering Time for Aqueous Slurries (25 grams Solid Contaminantin 100 grams 0.01 M KNO₃) Control + 0.5-1 grams Solid ControlSilane-Modified UF Resin Geltone* 13.1 seconds 8.2 (slurry pH) (8.1)(8.5) Bentonite 5.3 2.3 (slurry pH) (8.8) (8.8) Graphite 8.1 5.2 (slurrypH) (4.4) (4.5) Kaolin 10.5 5.4 (slurry pH) (3.3) (3.7) Talc (<10micron) 2.0 1.3 (slurry pH) (8.8) (8.9) *brand name for montmorilloniteclay

The above results demonstrate the ability of silane-modified UF resins,even when used in small quantities, to significantly decrease thedewatering time for a number of solid particles.

EXAMPLE 9

Another urea-formaldehyde (UF) resin, modified with a silane couplingagent as described above, was tested for its ability to reduce thedewatering time, by filtration, of solid contaminants suspended in anaqueous slurry. Filtration tests were conducted using the modified baseresin alone and in combination with polyacrylic acid (PAA) at variousratios. In each case, the initial filtration rate as well as the totaltime required for the filtration (i.e., the dewatering time), wasdetermined. Results are shown below in Table 7.

TABLE 7 Initial Filtration Rate and Dewatering Time for CarlsbadTailings Dewatering Agent Initial Total (Silane-Modified Filtration RateFiltration Time UF Resin/PAA) (grams/second) (seconds) 2 ml/0 ml 0.33 681 ml/2 ml 0.30 75.5 4 ml/1 ml 0.32 79 4 ml/2 ml 0.31 83.5 1 ml/1 ml 0.2588 0 ml/0 ml 0.16 158 0 ml/2 ml 0.11 203

The above results demonstrate the ability of silane-modified UF resins,when used either alone or with an additional dewatering agents, toimprove the dewatering of solids suspended in aqueous slurries.

EXAMPLE 10

The urea-formaldehyde base resin, denoted Resin F in Table 1 above, wasmodified by the substituted silane coupling agent #3(aminopropyltriethoxysilane, Silane A1100, available under the tradename Silquest (GE Silicones-OSi Specialties, Wilton, Conn., USA)), asdescribed above in Table 2. The modification of this base resins wasperformed according to procedures described above in Example 2.

The resulting modified amine-aldehyde resin was used to treat aqueousslurries of coal ore prior to cyclone separation operations, in order toevaluate cyclone separation efficiency at various resin addition levels.One cyclone separation operation processed relatively small coalparticles in the aqueous resin-treated feed (or sump) to a heavy mediumcyclone. A second cyclone separation operation processed relativelylarge coal particles in the aqueous resin-treated feed (or sump) to aclarifying cyclone. At each resin addition level, the purified coal,obtained as the combined product of these cyclones run in parallel, wasanalyzed for ash, sulfur, and mercury impurities, as well as moisturecontent and fuel value, measured in BTU per lb. The temperature of theslurries varied from 22-35° C., although any temperature at which theslurries are liquid (e.g., from 0-55° C.) could theoretically beemployed. The results of the coal purification study are summarized inTable 8 below.

TABLE 8 Cyclone Separation of Aqueous Coal Ore Slurries, at VariousAmine-Aldehyde Resin Addition Levels Hvy Med Clarifying PurifiedPurified Purified Cyclone, Cyclone, Coal Coal Coal Purified lb/ton resinlb/ton resin Ash, Sulfur Moisture Coal added added wt-% wt-% wt-% BTU/lb0 0 11.93 1.25 8.64 11,882 0.1 0.25 10.78 1.18 6.45 12,364 0.25 0.510.39 1.14 6.42 12,598

This study demonstrated the ability of the modified amine-aldehyde resinof the present invention to improve the product quality of coal that waspurified in size or density classification operations. The amounts ofash (containing siliceous clay materials), sulfur, and moisture in thepurified coal were less than the corresponding amounts obtained in thepurified coal (i.e., a reference coal) processed in the same cycloneoperations, but without addition of the resin. Consistent with theseresults, the fuel value of the purified coal increased with increasingaddition of the modified amine-aldehyde resin.

Although no trace mercury analyses were performed on the purified coal,it is believed that the predominant mercury-containing compound in thecoal ore was mercuric sulfide. The observed reduction in the sulfuramount, relative to the reference coal recovered in the cycloneseparation without added amine-aldehyde resin, would therefore beexpected to approximate the reduction in the mercury amount. Thus, a 5.6wt-% reduction in mercury would be expected to result from the use of0.1 lb/ton and 0.25 lb/ton resin added to the heavy medium cyclone feedand clarifying cyclone, respectively, as described in the experimentabove. Likewise, an 8.8 wt-% reduction in mercury would be expected toresult from the use of 0.25 lb/ton and 0.5 lb/ton resin added to theheavy medium cyclone feed and clarifying cyclone, respectively, also asdescribed in the experiment above.

EXAMPLE 11

The modified amine-aldehyde resin described above in Example 10 wastested for its ability to improve the efficiency of a coal beneficiationprocess using froth flotation. The resin was used to treat an aqueousslurry of impure coal ore, containing approximately 10-15 wt-% solids,by adding the resin at various addition levels. Treating of the slurryprior to the froth flotation step also included conditioning of theslurry by mixing the slurry with the added resin for about 4 minutes,prior to initiating froth flotation in a froth flotation cellconventionally used for coal. The amount of solids, expressed as aweight percentage, was measured in the product (overhead) stream fromthe froth flotation, carrying the purified coal. The moisture level ofthe purified coal (after screening) was also determined by analysis. Inthe “tailings” (or bottoms) stream carrying the solids that weredepressed in the froth flotation, the amount of solids, expressed as aweight percentage, was measured. Also measured were the amounts ofsulfur and ash impurities collected over a 1 hour period of steady stateoperation. A further analysis of the tailings stream was conducted todetermine the total amount of mercury in mg/liter. Three separate trialswere run, with a reference experiment performed in each trial with noadded modified amine-aldehyde resin. The results of this study aresummarized in Table 9 below.

TABLE 9 Froth Flotation of Aqueous Impure Coal Ore Slurries, at VariousAmine-Aldehyde Resin Addition Levels Aqueous slurry of Purified impurecoal Product Coal Tailings Tailings Tailings Tailings ore Stream Mois-Stream Stream Stream Stream lb/ton resin Solids, ture, Solids, Sulfur,Ash, Mercury, added wt-% wt-% wt-% lb/hr lb/hr mg/l TRIAL #1 0(reference) 37.2 12.7 1.13 41.92 222.4 0.0032 0.77 35.9 12.38 3.83 72.93281.92 0.0063 TRIAL #2 0 (reference) 37.05 12.25 1.62 46.82 183.68 n/a1.98 26.83 11.82 5.44 96.31 322.56 n/a TRIAL #3 0 (reference) 36.7611.13 1.27 41.10 150.72 0.0041 4.25 27.42 9.73 6.18 73.86 318.4 0.0058

The above results show that the amounts ash, sulfur, and mercuryimpurities increased in the tailings (containing the rejected ordepressed solids) in each case where the aqueous slurry of impure coalore was treated with the modified amine-aldehyde depressant, prior tofroth flotation. Moreover, the percentage increase in the ash impurity(containing non-combustible material such as siliceous clay) in thetailings appeared to broadly correlate with the amount of resin added,and the improved rejection of unwanted ash was consistent with theincrease in the solids level of the tailings stream. As discussed above,the observed increases in both mercury and sulfur in the tailings wereconsistent with the majority of the mercury impurity being in the formof mercuric sulfide.

The improved recovery of unwanted impurities in the tailings thereforetranslated to a higher quality purified coal in the product stream,relative to the reference experiments in which no resin depressant wasadded. Also, the moisture level in the purified coal was reduced in eachtrial by the addition of the resin depressant. The reduction in moisturecorrelated with the amount of resin added. Overall the above datademonstrates the advantages associated with using the modifiedamine-aldehyde resin as a depressant in the froth flotation of coal ore.

1. A modified urea-formaldehyde resin for use in solid/liquid separationprocesses comprising, a urea-formaldehye resin modified with a silanecoupling agent, wherein the urea-formaldehyde resin has a mole ratio ofurea:formaldehyde in the range of 1:2 to 1:3.
 2. The modified base resinof claim 1, wherein said base resin comprises a urea-formaldehyde resinhaving a number average molecular weight (M_(n)) of greater than about100 grams/mole.
 3. The modified base resin of claim 2, wherein said baseresin has a number average molecular weight (M_(n)) from about 400 toabout 4000 grams/mole.
 4. The modified base resin of claim 1, whereinsaid modified base resin is in the form of a solution or dispersionhaving a resin solids content from about 0.1% to about 90% by weight. 5.The modified base resin of claim 1, having a resin solids content ofgreater that about 90% by weight.
 6. The modified base resin of claim 5,wherein said modified base resin is in the form of solid powder, prill,lump, flake or melt.